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Class: CSV

Relationships & Source Files
Namespace Children
Modules:
Classes:
Exceptions:
Super Chains via Extension / Inclusion / Inheritance
Class Chain:
self, Forwardable
Instance Chain:
self, Enumerable
Inherits: Object
Defined in: lib/csv.rb,
lib/csv/delete_suffix.rb,
lib/csv/fields_converter.rb,
lib/csv/match_p.rb,
lib/csv/parser.rb,
lib/csv/row.rb,
lib/csv/table.rb,
lib/csv/version.rb,
lib/csv/writer.rb

Overview

CSV (comma-separated variables) data is a text representation of a table:

  • A row separator delimits table rows. A common row separator is the newline character "\n".

  • A column separator delimits fields in a row. A common column separator is the comma character ",".

This CSV String, with row separator "\n" and column separator ",", has three rows and two columns:

"foo,0\nbar,1\nbaz,2\n"

Despite the name CSV, a CSV representation can use different separators.

For more about tables, see the Wikipedia article “) {CSV::Table (information)}”, especially its section “Simple table

Class CSV

Class CSV provides methods for:

  • Parsing CSV data from a String object, a File (via its file path), or an IO object.

  • Generating CSV data to a String object.

To make CSV available:

require 'csv'

All examples here assume that this has been done.

Keeping It Simple

A CSV object has dozens of instance methods that offer fine-grained control of parsing and generating CSV data. For many needs, though, simpler approaches will do.

This section summarizes the singleton methods in CSV that allow you to parse and generate without explicitly creating CSV objects. For details, follow the links.

Simple Parsing

Parsing methods commonly return either of:

  • An Array of Arrays of Strings:

    • The outer Array is the entire “table”.

    • Each inner Array is a row.

    • Each String is a field.

  • A Table object. For details, see \ with Headers.

Parsing a String

The input to be parsed can be a string:

string = "foo,0\nbar,1\nbaz,2\n"

Method .parse returns the entire CSV data:

CSV.parse(string) # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

Method .parse_line returns only the first row:

CSV.parse_line(string) # => ["foo", "0"]

CSV extends class String with instance method String#parse_csv, which also returns only the first row:

string.parse_csv # => ["foo", "0"]
Parsing Via a File Path

The input to be parsed can be in a file:

string = "foo,0\nbar,1\nbaz,2\n"
path = 't.csv'
File.write(path, string)

Method .read returns the entire CSV data:

CSV.read(path) # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

Method .foreach iterates, passing each row to the given block:

CSV.foreach(path) do |row|
  p row
end

Output:

["foo", "0"]
["bar", "1"]
["baz", "2"]

Method .table returns the entire CSV data as a Table object:

CSV.table(path) # => #<CSV::Table mode:col_or_row row_count:3>
Parsing from an Open IO Stream

The input to be parsed can be in an open IO stream:

Method .read returns the entire CSV data:

File.open(path) do |file|
  CSV.read(file)
end # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

As does method .parse:

File.open(path) do |file|
  CSV.parse(file)
end # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

Method .parse_line returns only the first row:

File.open(path) do |file|
 CSV.parse_line(file)
end # => ["foo", "0"]

Method .foreach iterates, passing each row to the given block:

File.open(path) do |file|
  CSV.foreach(file) do |row|
    p row
  end
end

Output:

["foo", "0"]
["bar", "1"]
["baz", "2"]

Method .table returns the entire CSV data as a Table object:

File.open(path) do |file|
  CSV.table(file)
end # => #<CSV::Table mode:col_or_row row_count:3>

Simple Generating

Method .generate returns a String; this example uses method #<< to append the rows that are to be generated:

output_string = CSV.generate do |csv|
  csv << ['foo', 0]
  csv << ['bar', 1]
  csv << ['baz', 2]
end
output_string # => "foo,0\nbar,1\nbaz,2\n"

Method .generate_line returns a String containing the single row constructed from an Array:

CSV.generate_line(['foo', '0']) # => "foo,0\n"

CSV extends class Array with instance method Array#to_csv, which forms an Array into a String:

['foo', '0'].to_csv # => "foo,0\n"

“Filtering” CSV

Method .filter provides a Unix-style filter for CSV data. The input data is processed to form the output data:

in_string = "foo,0\nbar,1\nbaz,2\n"
out_string = ''
CSV.filter(in_string, out_string) do |row|
  row[0] = row[0].upcase
  row[1] *= 4
end
out_string # => "FOO,0000\nBAR,1111\nBAZ,2222\n"

CSV Objects

There are three ways to create a CSV object:

  • Method .new returns a new CSV object.

  • Method .instance returns a new or cached CSV object.

  • Method CSV() also returns a new or cached CSV object.

Instance Methods

CSV has three groups of instance methods:

  • Its own internally defined instance methods.

  • Methods included by module Enumerable.

  • Methods delegated to class IO. See below.

Delegated Methods

For convenience, a CSV object will delegate to many methods in class IO. (A few have wrapper “guard code” in CSV.) You may call:

  • IO#binmode

  • #binmode?

  • IO#close

  • IO#close_read

  • IO#close_write

  • IO#closed?

  • #eof

  • #eof?

  • IO#external_encoding

  • IO#fcntl

  • IO#fileno

  • #flock

  • IO#flush

  • IO#fsync

  • IO#internal_encoding

  • #ioctl

  • IO#isatty

  • #path

  • IO#pid

  • IO#pos

  • IO#pos=

  • IO#reopen

  • #rewind

  • IO#seek

  • #stat

  • IO#string

  • IO#sync

  • IO#sync=

  • IO#tell

  • #to_i

  • #to_io

  • IO#truncate

  • IO#tty?

Options

The default values for options are:

DEFAULT_OPTIONS = {
  # For both parsing and generating.
  col_sep:            ",",
  row_sep:            :auto,
  quote_char:         '"',
  # For parsing.
  field_size_limit:   nil,
  converters:         nil,
  unconverted_fields: nil,
  headers:            false,
  return_headers:     false,
  header_converters:  nil,
  skip_blanks:        false,
  skip_lines:         nil,
  liberal_parsing:    false,
  nil_value:          nil,
  empty_value:        "",
  # For generating.
  write_headers:      nil,
  quote_empty:        true,
  force_quotes:       false,
  write_converters:   nil,
  write_nil_value:    nil,
  write_empty_value:  "",
  strip:              false,
}
Options for Parsing

Options for parsing, described in detail below, include:

  • #row_sep: Specifies the row separator; used to delimit rows.

  • #col_sep: Specifies the column separator; used to delimit fields.

  • #quote_char: Specifies the quote character; used to quote fields.

  • #field_size_limit: Specifies the maximum field size allowed.

  • #converters: Specifies the field converters to be used.

  • unconverted_fields: Specifies whether unconverted fields are to be available.

  • #headers: Specifies whether data contains headers, or specifies the headers themselves.

  • return_headers: Specifies whether headers are to be returned.

  • #header_converters: Specifies the header converters to be used.

  • skip_blanks: Specifies whether blanks lines are to be ignored.

  • #skip_lines: Specifies how comments lines are to be recognized.

  • strip: Specifies whether leading and trailing whitespace are to be stripped from fields..

  • liberal_parsing: Specifies whether CSV should attempt to parse non-compliant data.

  • nil_value: Specifies the object that is to be substituted for each null (no-text) field.

  • empty_value: Specifies the object that is to be substituted for each empty field.

Options for Generating

Options for generating, described in detail below, include:

  • #row_sep: Specifies the row separator; used to delimit rows.

  • #col_sep: Specifies the column separator; used to delimit fields.

  • #quote_char: Specifies the quote character; used to quote fields.

  • write_headers: Specifies whether headers are to be written.

  • force_quotes: Specifies whether each output field is to be quoted.

  • quote_empty: Specifies whether each empty output field is to be quoted.

  • write_converters: Specifies the field converters to be used in writing.

  • write_nil_value: Specifies the object that is to be substituted for each nil-valued field.

  • write_empty_value: Specifies the object that is to be substituted for each empty field.

CSV with Headers

CSV allows to specify column names of CSV file, whether they are in data, or provided separately. If headers are specified, reading methods return an instance of Table, consisting of Row.

# Headers are part of data
data = CSV.parse(<<~ROWS, headers: true)
  Name,Department,Salary
  Bob,Engineering,1000
  Jane,Sales,2000
  John,Management,5000
ROWS

data.class      #=> CSV::Table
data.first      #=> #<CSV::Row "Name":"Bob" "Department":"Engineering" "Salary":"1000">
data.first.to_h #=> {"Name"=>"Bob", "Department"=>"Engineering", "Salary"=>"1000"}

# Headers provided by developer
data = CSV.parse('Bob,Engineering,1000', headers: %i[name department salary])
data.first      #=> #<CSV::Row name:"Bob" department:"Engineering" salary:"1000">

Converters

By default, each value (field or header) parsed by CSV is formed into a String. You can use a field converter or header converter to intercept and modify the parsed values:

Also by default, each value to be written during generation is written 'as-is'. You can use a write converter to modify values before writing.

Specifying Converters

You can specify converters for parsing or generating in the options argument to various CSV methods:

  • Option #converters for converting parsed field values.

  • Option #header_converters for converting parsed header values.

  • Option write_converters for converting values to be written (generated).

There are three forms for specifying converters:

  • A converter proc: executable code to be used for conversion.

  • A converter name: the name of a stored converter.

  • A converter list: an array of converter procs, converter names, and converter lists.

Converter Procs

This converter proc, strip_converter, accepts a value field and returns field.strip:

strip_converter = proc {|field| field.strip }

In this call to .parse, the keyword argument converters: string_converter specifies that:

  • Proc string_converter is to be called for each parsed field.

  • The converter's return value is to replace the field value.

Example:

string = " foo , 0 \n bar , 1 \n baz , 2 \n"
array = CSV.parse(string, converters: strip_converter)
array # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

A converter proc can receive a second argument, field_info, that contains details about the field. This modified strip_converter displays its arguments:

strip_converter = proc do |field, field_info|
  p [field, field_info]
  field.strip
end
string = " foo , 0 \n bar , 1 \n baz , 2 \n"
array = CSV.parse(string, converters: strip_converter)
array # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

Output:

[" foo ", #<struct CSV::FieldInfo index=0, line=1, header=nil>]
[" 0 ", #<struct CSV::FieldInfo index=1, line=1, header=nil>]
[" bar ", #<struct CSV::FieldInfo index=0, line=2, header=nil>]
[" 1 ", #<struct CSV::FieldInfo index=1, line=2, header=nil>]
[" baz ", #<struct CSV::FieldInfo index=0, line=3, header=nil>]
[" 2 ", #<struct CSV::FieldInfo index=1, line=3, header=nil>]

Each CSV::Info object shows:

  • The 0-based field index.

  • The 1-based line index.

  • The field header, if any.

Stored Converters

A converter may be given a name and stored in a structure where the parsing methods can find it by name.

The storage structure for field converters is the Hash Converters. It has several built-in converter procs:

  • :integer: converts each String-embedded integer into a true Integer.

  • :float: converts each String-embedded float into a true Float.

  • :date: converts each String-embedded date into a true Date.

  • :date_time: converts each String-embedded date-time into a true DateTime

. This example creates a converter proc, then stores it:

strip_converter = proc {|field| field.strip }
CSV::Converters[:strip] = strip_converter

Then the parsing method call can refer to the converter by its name, :strip:

string = " foo , 0 \n bar , 1 \n baz , 2 \n"
array = CSV.parse(string, converters: :strip)
array # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

The storage structure for header converters is the Hash HeaderConverters, which works in the same way. It also has built-in converter procs:

  • :downcase: Downcases each header.

  • :symbol: Converts each header to a Symbol.

There is no such storage structure for write headers.

Converter Lists

A converter list is an Array that may include any assortment of:

  • Converter procs.

  • Names of stored converters.

  • Nested converter lists.

Examples:

numeric_converters = [:integer, :float]
date_converters = [:date, :date_time]
[numeric_converters, strip_converter]
[strip_converter, date_converters, :float]

Like a converter proc, a converter list may be named and stored in either CSV::Converters or HeaderConverters:

CSV::Converters[:custom] = [strip_converter, date_converters, :float]
CSV::HeaderConverters[:custom] = [:downcase, :symbol]

There are two built-in converter lists:

CSV::Converters[:numeric] # => [:integer, :float]
CSV::Converters[:all] # => [:date_time, :numeric]
Field Converters

With no conversion, all parsed fields in all rows become Strings:

string = "foo,0\nbar,1\nbaz,2\n"
ary = CSV.parse(string)
ary # => # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

When you specify a field converter, each parsed field is passed to the converter; its return value becomes the stored value for the field. A converter might, for example, convert an integer embedded in a String into a true Integer. (In fact, that's what built-in field converter :integer does.)

There are three ways to use field converters.

  • Using option converters with a parsing method:

    ary = CSV.parse(string, converters: :integer)
    ary # => [0, 1, 2] # => [["foo", 0], ["bar", 1], ["baz", 2]]
  • Using option converters with a new CSV instance:

    csv = CSV.new(string, converters: :integer)
    # Field converters in effect:
    csv.converters # => [:integer]
    csv.read # => [["foo", 0], ["bar", 1], ["baz", 2]]
  • Using method #convert to add a field converter to a CSV instance:

    csv = CSV.new(string)
    # Add a converter.
    csv.convert(:integer)
    csv.converters # => [:integer]
    csv.read # => [["foo", 0], ["bar", 1], ["baz", 2]]

Installing a field converter does not affect already-read rows:

csv = CSV.new(string)
csv.shift # => ["foo", "0"]
# Add a converter.
csv.convert(:integer)
csv.converters # => [:integer]
csv.read # => [["bar", 1], ["baz", 2]]

There are additional built-in converters, and custom converters are also supported.

Built-In Field Converters

The built-in field converters are in Hash Converters:

  • Each key is a field converter name.

  • Each value is one of:

    • A Proc field converter.

    • An Array of field converter names.

Display:

CSV::Converters.each_pair do |name, value|
  if value.kind_of?(Proc)
    p [name, value.class]
  else
    p [name, value]
  end
end

Output:

[:integer, Proc]
[:float, Proc]
[:numeric, [:integer, :float]]
[:date, Proc]
[:date_time, Proc]
[:all, [:date_time, :numeric]]

Each of these converters transcodes values to UTF-8 before attempting conversion. If a value cannot be transcoded to UTF-8 the conversion will fail and the value will remain unconverted.

Converter :integer converts each field that Integer() accepts:

data = '0,1,2,x'
# Without the converter
csv = CSV.parse_line(data)
csv # => ["0", "1", "2", "x"]
# With the converter
csv = CSV.parse_line(data, converters: :integer)
csv # => [0, 1, 2, "x"]

Converter :float converts each field that Float() accepts:

data = '1.0,3.14159,x'
# Without the converter
csv = CSV.parse_line(data)
csv # => ["1.0", "3.14159", "x"]
# With the converter
csv = CSV.parse_line(data, converters: :float)
csv # => [1.0, 3.14159, "x"]

Converter :numeric converts with both :integer and :float..

Converter :date converts each field that Date.parse accepts:

data = '2001-02-03,x'
# Without the converter
csv = CSV.parse_line(data)
csv # => ["2001-02-03", "x"]
# With the converter
csv = CSV.parse_line(data, converters: :date)
csv # => [#<Date: 2001-02-03 ((2451944j,0s,0n),+0s,2299161j)>, "x"]

Converter :date_time converts each field that DateTime.parse accepts:

data = '2020-05-07T14:59:00-05:00,x'
# Without the converter
csv = CSV.parse_line(data)
csv # => ["2020-05-07T14:59:00-05:00", "x"]
# With the converter
csv = CSV.parse_line(data, converters: :date_time)
csv # => [#<DateTime: 2020-05-07T14:59:00-05:00 ((2458977j,71940s,0n),-18000s,2299161j)>, "x"]

Converter :numeric converts with both :date_time and :numeric..

As seen above, method #convert adds converters to a CSV instance, and method #converters returns an Array of the converters in effect:

csv = CSV.new('0,1,2')
csv.converters # => []
csv.convert(:integer)
csv.converters # => [:integer]
csv.convert(:date)
csv.converters # => [:integer, :date]
Custom Field Converters

You can define a custom field converter:

strip_converter = proc {|field| field.strip }
string = " foo , 0 \n bar , 1 \n baz , 2 \n"
array = CSV.parse(string, converters: strip_converter)
array # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

You can register the converter in Converters Hash, which allows you to refer to it by name:

CSV::Converters[:strip] = strip_converter
string = " foo , 0 \n bar , 1 \n baz , 2 \n"
array = CSV.parse(string, converters: :strip)
array # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]
Header Converters

Header converters operate only on headers (and not on other rows).

There are three ways to use header converters; these examples use built-in header converter :dowhcase, which downcases each parsed header.

  • Option #header_converters with a singleton parsing method:

    string = "Name,Count\nFoo,0\n,Bar,1\nBaz,2"
    tbl = CSV.parse(string, headers: true, header_converters: :downcase)
    tbl.class # => CSV::Table
    tbl.headers # => ["name", "count"]
  • Option #header_converters with a new CSV instance:

    csv = CSV.new(string, header_converters: :downcase)
    # Header converters in effect:
    csv.header_converters # => [:downcase]
    tbl = CSV.parse(string, headers: true)
    tbl.headers # => ["Name", "Count"]
  • Method #header_convert adds a header converter to a CSV instance:

    csv = CSV.new(string)
    # Add a header converter.
    csv.header_convert(:downcase)
    csv.header_converters # => [:downcase]
    tbl = CSV.parse(string, headers: true)
    tbl.headers # => ["Name", "Count"]
Built-In Header Converters

The built-in header converters are in Hash HeaderConverters. The keys there are the names of the converters:

CSV::HeaderConverters.keys # => [:downcase, :symbol]

Converter :downcase converts each header by downcasing it:

string = "Name,Count\nFoo,0\n,Bar,1\nBaz,2"
tbl = CSV.parse(string, headers: true, header_converters: :downcase)
tbl.class # => CSV::Table
tbl.headers # => ["name", "count"]

Converter :symbol converts each header by making it into a Symbol:

string = "Name,Count\nFoo,0\n,Bar,1\nBaz,2"
tbl = CSV.parse(string, headers: true, header_converters: :symbol)
tbl.headers # => [:name, :count]

Details:

  • Strips leading and trailing whitespace.

  • Downcases the header.

  • Replaces embedded spaces with underscores.

  • Removes non-word characters.

  • Makes the string into a Symbol.

Custom Header Converters

You can define a custom header converter:

upcase_converter = proc {|header| header.upcase }
string = "Name,Value\nfoo,0\nbar,1\nbaz,2\n"
table = CSV.parse(string, headers: true, header_converters: upcase_converter)
table # => #<CSV::Table mode:col_or_row row_count:4>
table.headers # => ["NAME", "VALUE"]

You can register the converter in HeaderConverters Hash, which allows you to refer to it by name:

CSV::HeaderConverters[:upcase] = upcase_converter
table = CSV.parse(string, headers: true, header_converters: :upcase)
table # => #<CSV::Table mode:col_or_row row_count:4>
table.headers # => ["NAME", "VALUE"]
Write Converters

When you specify a write converter for generating CSV, each field to be written is passed to the converter; its return value becomes the new value for the field. A converter might, for example, strip whitespace from a field.

Using no write converter (all fields unmodified):

output_string = CSV.generate do |csv|
  csv << [' foo ', 0]
  csv << [' bar ', 1]
  csv << [' baz ', 2]
end
output_string # => " foo ,0\n bar ,1\n baz ,2\n"

Using option write_converters with two custom write converters:

strip_converter = proc {|field| field.respond_to?(:strip) ? field.strip : field }
upcase_converter = proc {|field| field.respond_to?(:upcase) ? field.upcase : field }
write_converters = [strip_converter, upcase_converter]
output_string = CSV.generate(write_converters: write_converters) do |csv|
  csv << [' foo ', 0]
  csv << [' bar ', 1]
  csv << [' baz ', 2]
end
output_string # => "FOO,0\nBAR,1\nBAZ,2\n"

Character Encodings (M17n or Multilingualization)

This new CSV parser is m17n savvy. The parser works in the Encoding of the IO or ::String object being read from or written to. Your data is never transcoded (unless you ask Ruby to transcode it for you) and will literally be parsed in the Encoding it is in. Thus CSV will return Arrays or Rows of Strings in the Encoding of your data. This is accomplished by transcoding the parser itself into your Encoding.

Some transcoding must take place, of course, to accomplish this multiencoding support. For example, :col_sep, :row_sep, and :quote_char must be transcoded to match your data. Hopefully this makes the entire process feel transparent, since CSV's defaults should just magically work for your data. However, you can set these values manually in the target Encoding to avoid the translation.

It's also important to note that while all of CSV's core parser is now Encoding agnostic, some features are not. For example, the built-in converters will try to transcode data to UTF-8 before making conversions. Again, you can provide custom converters that are aware of your Encodings to avoid this translation. It's just too hard for me to support native conversions in all of Ruby's Encodings.

Anyway, the practical side of this is simple: make sure IO and ::String objects passed into CSV have the proper Encoding set and everything should just work. CSV methods that allow you to open IO objects (CSV::foreach(), .open(), .read(), and .readlines()) do allow you to specify the Encoding.

One minor exception comes when generating CSV into a ::String with an Encoding that is not ASCII compatible. There's no existing data for CSV to use to prepare itself and thus you will probably need to manually specify the desired Encoding for most of those cases. It will try to guess using the fields in a row of output though, when using .generate_line() or Array#to_csv().

I try to point out any other Encoding issues in the documentation of methods as they come up.

This has been tested to the best of my ability with all non-“dummy” Encodings Ruby ships with. However, it is brave new code and may have some bugs. Please feel free to report any issues you find with it.

Constant Summary

  • ConverterEncoding =

    The encoding used by all converters.

    # File 'lib/csv.rb', line 863
    Encoding.find("UTF-8")
  • Converters =

    A Hash containing the names and Procs for the built-in field converters. See Built-In Field Converters.

    This Hash is intentionally left unfrozen, and may be extended with custom field converters. See Custom Field Converters.

    # File 'lib/csv.rb', line 871
    {
      integer:   lambda { |f|
        Integer(f.encode(ConverterEncoding)) rescue f
      },
      float:     lambda { |f|
        Float(f.encode(ConverterEncoding)) rescue f
      },
      numeric:   [:integer, :float],
      date:      lambda { |f|
        begin
          e = f.encode(ConverterEncoding)
          e.match?(DateMatcher) ? Date.parse(e) : f
        rescue  # encoding conversion or date parse errors
          f
        end
      },
      date_time: lambda { |f|
        begin
          e = f.encode(ConverterEncoding)
          e.match?(DateTimeMatcher) ? DateTime.parse(e) : f
        rescue  # encoding conversion or date parse errors
          f
        end
      },
      all:       [:date_time, :numeric],
    }
  • DEFAULT_OPTIONS =

    Default values for method options.

    # File 'lib/csv.rb', line 912
    {
      # For both parsing and generating.
      col_sep:            ",",
      row_sep:            :auto,
      quote_char:         '"',
      # For parsing.
      field_size_limit:   nil,
      converters:         nil,
      unconverted_fields: nil,
      headers:            false,
      return_headers:     false,
      header_converters:  nil,
      skip_blanks:        false,
      skip_lines:         nil,
      liberal_parsing:    false,
      nil_value:          nil,
      empty_value:        "",
      # For generating.
      write_headers:      nil,
      quote_empty:        true,
      force_quotes:       false,
      write_converters:   nil,
      write_nil_value:    nil,
      write_empty_value:  "",
      strip:              false,
    }.freeze
  • DateMatcher =

    A Regexp used to find and convert some common Date formats.

    # File 'lib/csv.rb', line 851
    / \A(?: (\w,?\s)?\w\s\d{1,2},?\s+\d{2,4} |
    \d{4}-\d{2}-\d{2} )\z /x
  • DateTimeMatcher =

    A Regexp used to find and convert some common DateTime formats.

    # File 'lib/csv.rb', line 854
    / \A(?: (\w,?\s)?\w\s\d{1,2}\s\d{1,2}:\d{1,2}:\d{1,2},?\s\d{2,4} |
        \d{4}-\d{2}-\d{2}\s\d{2}:\d{2}:\d{2} |
        # ISO-8601
        \d{4}-\d{2}-\d{2}
          (?:T\d{2}:\d{2}(?::\d{2}(?:\.\d)?(?:[-]\d{2}(?::\d{2})|Z)?)?)?
    )\z /x
  • HeaderConverters =

    A Hash containing the names and Procs for the built-in header converters. See Built-In Header Converters.

    This Hash is intentionally left unfrozen, and may be extended with custom field converters. See Custom Header Converters.

    # File 'lib/csv.rb', line 904
    {
      downcase: lambda { |h| h.encode(ConverterEncoding).downcase },
      symbol:   lambda { |h|
        h.encode(ConverterEncoding).downcase.gsub(/[^\s\w]+/, "").strip.
                                             gsub(/\s+/, "_").to_sym
      }
    }
  • VERSION =

    The version of the installed library.

    # File 'lib/csv/version.rb', line 5
    "3.1.9"

Class Method Summary

Instance Attribute Summary

Instance Method Summary

Constructor Details

.new(string) ⇒ CSV .new(io) ⇒ CSV .new(string, **options) ⇒ CSV .new(io, **options) ⇒ CSV

Returns the new CSV object created using string or io and the specified options.

  • Argument string should be a String object; it will be put into a new StringIO object positioned at the beginning.

In addition to the CSV instance methods, several IO methods are delegated. See Delegated Methods.


Create a CSV object from a String object:

csv = CSV.new('foo,0')
csv # => #<CSV io_type:StringIO encoding:UTF-8 lineno:0 col_sep:"," row_sep:"\n" quote_char:"\"">

Create a CSV object from a File object:

File.write('t.csv', 'foo,0')
csv = CSV.new(File.open('t.csv'))
csv # => #<CSV io_type:File io_path:"t.csv" encoding:UTF-8 lineno:0 col_sep:"," row_sep:"\n" quote_char:"\"">

Raises an exception if the argument is nil:

# Raises ArgumentError (Cannot parse nil as CSV):
CSV.new(nil)

Raises:

  • (ArgumentError)
[ GitHub ]

  
# File 'lib/csv.rb', line 1732

def initialize(data,
               col_sep: ",",
               row_sep: :auto,
               quote_char: '"',
               field_size_limit: nil,
               converters: nil,
               unconverted_fields: nil,
               headers: false,
               return_headers: false,
               write_headers: nil,
               header_converters: nil,
               skip_blanks: false,
               force_quotes: false,
               skip_lines: nil,
               liberal_parsing: false,
               internal_encoding: nil,
               external_encoding: nil,
               encoding: nil,
               nil_value: nil,
               empty_value: "",
               quote_empty: true,
               write_converters: nil,
               write_nil_value: nil,
               write_empty_value: "",
               strip: false)
  raise ArgumentError.new("Cannot parse nil as CSV") if data.nil?

  if data.is_a?(String)
    @io = StringIO.new(data)
    @io.set_encoding(encoding || data.encoding)
  else
    @io = data
  end
  @encoding = determine_encoding(encoding, internal_encoding)

  @base_fields_converter_options = {
    nil_value: nil_value,
    empty_value: empty_value,
  }
  @write_fields_converter_options = {
    nil_value: write_nil_value,
    empty_value: write_empty_value,
  }
  @initial_converters = converters
  @initial_header_converters = header_converters
  @initial_write_converters = write_converters

  @parser_options = {
    column_separator: col_sep,
    row_separator: row_sep,
    quote_character: quote_char,
    field_size_limit: field_size_limit,
    unconverted_fields: unconverted_fields,
    headers: headers,
    return_headers: return_headers,
    skip_blanks: skip_blanks,
    skip_lines: skip_lines,
    liberal_parsing: liberal_parsing,
    encoding: @encoding,
    nil_value: nil_value,
    empty_value: empty_value,
    strip: strip,
  }
  @parser = nil
  @parser_enumerator = nil
  @eof_error = nil

  @writer_options = {
    encoding: @encoding,
    force_encoding: (not encoding.nil?),
    force_quotes: force_quotes,
    headers: headers,
    write_headers: write_headers,
    column_separator: col_sep,
    row_separator: row_sep,
    quote_character: quote_char,
    quote_empty: quote_empty,
  }

  @writer = nil
  writer if @writer_options[:write_headers]
end

Class Method Details

.filter(**options) {|row| ... } .filter(in_string, **options) {|row| ... } .filter(in_io, **options) {|row| ... } .filter(in_string, out_string, **options) {|row| ... } .filter(in_string, out_io, **options) {|row| ... } .filter(in_io, out_string, **options) {|row| ... } .filter(in_io, out_io, **options) {|row| ... }

Reads CSV input and writes CSV output.

For each input row:

  • Forms the data into:

    • A CSV::Row object, if headers are in use.

    • An Array of Arrays, otherwise.

  • Calls the block with that object.

  • Appends the block's return value to the output.

Arguments:

  • CSV source:

    • Argument in_string, if given, should be a String object; it will be put into a new StringIO object positioned at the beginning.

    • Argument in_io, if given, should be an IO object that is open for reading; on return, the IO object will be closed.

    • If neither in_string nor in_io is given, the input stream defaults to ARGF.

  • CSV output:

    • Argument out_string, if given, should be a String object; it will be put into a new StringIO object positioned at the beginning.

    • Argument out_io, if given, should be an IO object that is ppen for writing; on return, the IO object will be closed.

    • If neither out_string nor out_io is given, the output stream defaults to $stdout.

  • Argument options should be keyword arguments.

    • Each argument name that is prefixed with in_ or input_ is stripped of its prefix and is treated as an option for parsing the input. Option input_row_sep defaults to $INPUT_RECORD_SEPARATOR.

    • Each argument name that is prefixed with out_ or output_ is stripped of its prefix and is treated as an option for generating the output. Option output_row_sep defaults to $INPUT_RECORD_SEPARATOR.

    • Each argument not prefixed as above is treated as an option both for parsing the input and for generating the output.

    • See Options for Parsing and Options for Generating.

Example:

in_string = "foo,0\nbar,1\nbaz,2\n"
out_string = ''
CSV.filter(in_string, out_string) do |row|
  row[0] = row[0].upcase
  row[1] *= 4
end
out_string # => "FOO,0000\nBAR,1111\nBAZ,2222\n"
[ GitHub ]

  
# File 'lib/csv.rb', line 1052

def filter(input=nil, output=nil, **options)
  # parse options for input, output, or both
  in_options, out_options = Hash.new, {row_sep: $INPUT_RECORD_SEPARATOR}
  options.each do |key, value|
    case key.to_s
    when /\Ain(?:put)?_(.+)\Z/
      in_options[$1.to_sym] = value
    when /\Aout(?:put)?_(.+)\Z/
      out_options[$1.to_sym] = value
    else
      in_options[key]  = value
      out_options[key] = value
    end
  end

  # build input and output wrappers
  input  = new(input  || ARGF, **in_options)
  output = new(output || $stdout, **out_options)

  # process headers
  need_manual_header_output =
    (in_options[:headers] and
     out_options[:headers] == true and
     out_options[:write_headers])
  if need_manual_header_output
    first_row = input.shift
    if first_row
      if first_row.is_a?(Row)
        headers = first_row.headers
        yield headers
        output << headers
      end
      yield first_row
      output << first_row
    end
  end

  # read, yield, write
  input.each do |row|
    yield row
    output << row
  end
end

.foreach(path, mode='r', **options) {|row| ... ) .foreach(io, mode='r', **options {|row| ... ) .foreach(path, mode='r', headers: ..., **options) {|row| ... ) .foreach(io, mode='r', headers: ..., **options {|row| ... ) .foreach(path, mode = 'r', **options) ⇒ Enumerator .foreach(io, mode = 'r', **options) ⇒ Enumerator

Calls the block with each row read from source #path or io.

  • Argument #path, if given, must be the path to a file.

  • Argument mode, if given, must be a File mode See [Open Mode](IO.html#method-c-new-label-Open+Mode).

  • Arguments **options must be keyword options. See Options for Parsing.

  • This method optionally accepts an additional :encoding option that you can use to specify the Encoding of the data read from path or io. You must provide this unless your data is in the encoding given by Encoding.default_external. Parsing will use this to determine how to parse the data. You may provide a second Encoding to have the data transcoded as it is read. For example,

    encoding: 'UTF-32BE:UTF-8'

    would read UTF-32BE data from the file but transcode it to UTF-8 before parsing.

Without Option #headers

Without option #headers, returns each row as an Array object.

These examples assume prior execution of:

string = "foo,0\nbar,1\nbaz,2\n"
path = 't.csv'
File.write(path, string)

Read rows from a file at #path:

CSV.foreach(path) {|row| p row }

Output:

["foo", "0"]
["bar", "1"]
["baz", "2"]

Read rows from an IO object:

File.open(path) do |file|
  CSV.foreach(file) {|row| p row }
end

Output:

["foo", "0"]
["bar", "1"]
["baz", "2"]

Returns a new Enumerator if no block given:

CSV.foreach(path) # => #<Enumerator: CSV:foreach("t.csv", "r")>
CSV.foreach(File.open(path)) # => #<Enumerator: CSV:foreach(#<File:t.csv>, "r")>

Issues a warning if an encoding is unsupported:

CSV.foreach(File.open(path), encoding: 'foo:bar') {|row| }

Output:

warning: Unsupported encoding foo ignored
warning: Unsupported encoding bar ignored
With Option #headers

With option #headers, returns each row as a ::CSV::Row object.

These examples assume prior execution of:

string = "Name,Count\nfoo,0\nbar,1\nbaz,2\n"
path = 't.csv'
File.write(path, string)

Read rows from a file at #path:

CSV.foreach(path, headers: true) {|row| p row }

Output:

#<CSV::Row "Name":"foo" "Count":"0">
#<CSV::Row "Name":"bar" "Count":"1">
#<CSV::Row "Name":"baz" "Count":"2">

Read rows from an IO object:

File.open(path) do |file|
  CSV.foreach(file, headers: true) {|row| p row }
end

Output:

#<CSV::Row "Name":"foo" "Count":"0">
#<CSV::Row "Name":"bar" "Count":"1">
#<CSV::Row "Name":"baz" "Count":"2">

Raises an exception if #path is a String, but not the path to a readable file:

# Raises Errno::ENOENT (No such file or directory @ rb_sysopen - nosuch.csv):
CSV.foreach('nosuch.csv') {|row| }

Raises an exception if io is an IO object, but not open for reading:

io = File.open(path, 'w') {|row| }
# Raises TypeError (no implicit conversion of nil into String):
CSV.foreach(io) {|row| }

Raises an exception if mode is invalid:

# Raises ArgumentError (invalid access mode nosuch):
CSV.foreach(path, 'nosuch') {|row| }
[ GitHub ]

  
# File 'lib/csv.rb', line 1203

def foreach(path, mode="r", **options, &block)
  return to_enum(__method__, path, mode, **options) unless block_given?
  open(path, mode, **options) do |csv|
    csv.each(&block)
  end
end

.generate(csv_string, **options) {|csv| ... } .generate(**options) {|csv| ... }

  • Argument csv_string, if given, must be a String object; defaults to a new empty String.

  • Arguments options, if given, should be generating options. See Options for Generating.


Creates a new CSV object via CSV.new(csv_string, **options); calls the block with the CSV object, which the block may modify; returns the String generated from the CSV object.

Note that a passed String is modified by this method. Pass csv_string.dup if the String must be preserved.

This method has one additional option: :encoding, which sets the base Encoding for the output if no no str is specified. CSV needs this hint if you plan to output non-ASCII compatible data.


Add lines:

input_string = "foo,0\nbar,1\nbaz,2\n"
output_string = CSV.generate(input_string) do |csv|
  csv << ['bat', 3]
  csv << ['bam', 4]
end
output_string # => "foo,0\nbar,1\nbaz,2\nbat,3\nbam,4\n"
input_string # => "foo,0\nbar,1\nbaz,2\nbat,3\nbam,4\n"
output_string.equal?(input_string) # => true # Same string, modified

Add lines into new string, preserving old string:

input_string = "foo,0\nbar,1\nbaz,2\n"
output_string = CSV.generate(input_string.dup) do |csv|
  csv << ['bat', 3]
  csv << ['bam', 4]
end
output_string # => "foo,0\nbar,1\nbaz,2\nbat,3\nbam,4\n"
input_string # => "foo,0\nbar,1\nbaz,2\n"
output_string.equal?(input_string) # => false # Different strings

Create lines from nothing:

output_string = CSV.generate do |csv|
  csv << ['foo', 0]
  csv << ['bar', 1]
  csv << ['baz', 2]
end
output_string # => "foo,0\nbar,1\nbaz,2\n"

Raises an exception if csv_string is not a String object:

# Raises TypeError (no implicit conversion of Integer into String)
CSV.generate(0)

Yields:

  • (csv)
[ GitHub ]

  
# File 'lib/csv.rb', line 1269

def generate(str=nil, **options)
  encoding = options[:encoding]
  # add a default empty String, if none was given
  if str
    str = StringIO.new(str)
    str.seek(0, IO::SEEK_END)
    str.set_encoding(encoding) if encoding
  else
    str = +""
    str.force_encoding(encoding) if encoding
  end
  csv = new(str, **options) # wrap
  yield csv         # yield for appending
  csv.string        # return final String
end

.generate_line(ary) .generate_line(ary, **options)

Returns the String created by generating CSV from ary using the specified options.

Argument ary must be an Array.

Special options:

  • Option :row_sep defaults to $INPUT_RECORD_SEPARATOR ($/).:

    $INPUT_RECORD_SEPARATOR # => "\n"
  • This method accepts an additional option, :encoding, which sets the base Encoding for the output. This method will try to guess your Encoding from the first non-nil field in row, if possible, but you may need to use this parameter as a backup plan.

For other options, see Options for Generating.


Returns the String generated from an Array:

CSV.generate_line(['foo', '0']) # => "foo,0\n"

Raises an exception if ary is not an Array:

# Raises NoMethodError (undefined method `find' for :foo:Symbol)
CSV.generate_line(:foo)
[ GitHub ]

  
# File 'lib/csv.rb', line 1317

def generate_line(row, **options)
  options = {row_sep: $INPUT_RECORD_SEPARATOR}.merge(options)
  str = +""
  if options[:encoding]
    str.force_encoding(options[:encoding])
  else
    fallback_encoding = nil
    output_encoding = nil
    row.each do |field|
      next unless field.is_a?(String)
      fallback_encoding ||= field.encoding
      next if field.ascii_only?
      output_encoding = field.encoding
      break
    end
    output_encoding ||= fallback_encoding
    if output_encoding
      str.force_encoding(output_encoding)
    end
  end
  (new(str, **options) << row).string
end

.instance(string, **options) .instance(io = $stdout, **options) .instance(string, **options) {|csv| ... } .instance(io = $stdout, **options) {|csv| ... }

Creates or retrieves cached CSV objects. For arguments and options, see .new.


With no block given, returns a CSV object.

The first call to instance creates and caches a CSV object:

s0 = 's0'
csv0 = CSV.instance(s0)
csv0.class # => CSV

Subsequent calls to instance with that same string or io retrieve that same cached object:

csv1 = CSV.instance(s0)
csv1.class # => CSV
csv1.equal?(csv0) # => true # Same CSV object

A subsequent call to instance with a different string or io creates and caches a different CSV object.

s1 = 's1'
csv2 = CSV.instance(s1)
csv2.equal?(csv0) # => false # Different CSV object

All the cached objects remains available:

csv3 = CSV.instance(s0)
csv3.equal?(csv0) # true # Same CSV object
csv4 = CSV.instance(s1)
csv4.equal?(csv2) # true # Same CSV object

When a block is given, calls the block with the created or retrieved CSV object; returns the block's return value:

CSV.instance(s0) {|csv| :foo } # => :foo
[ GitHub ]

  
# File 'lib/csv.rb', line 981

def instance(data = $stdout, **options)
  # create a _signature_ for this method call, data object and options
  sig = [data.object_id] +
        options.values_at(*DEFAULT_OPTIONS.keys.sort_by { |sym| sym.to_s })

  # fetch or create the instance for this signature
  @@instances ||= Hash.new
  instance = (@@instances[sig] ||= new(data, **options))

  if block_given?
    yield instance  # run block, if given, returning result
  else
    instance        # or return the instance
  end
end

.open(file_path, mode = "rb", **options) ⇒ CSV .open(io, mode = "rb", **options) ⇒ CSV .open(file_path, mode = "rb", **options) {|csv| ... } ⇒ Object .open(io, mode = "rb", **options) {|csv| ... } ⇒ Object

possible options elements:

hash form:
  :invalid => nil      # raise error on invalid byte sequence (default)
  :invalid => :replace # replace invalid byte sequence
  :undef => :replace   # replace undefined conversion
  :replace => string   # replacement string ("?" or "\uFFFD" if not specified)
  • Argument #path, if given, must be the path to a file.

  • Argument mode, if given, must be a File mode See [Open Mode](IO.html#method-c-new-label-Open+Mode).

  • Arguments **options must be keyword options. See Options for Generating.

  • This method optionally accepts an additional :encoding option that you can use to specify the Encoding of the data read from path or io. You must provide this unless your data is in the encoding given by Encoding.default_external. Parsing will use this to determine how to parse the data. You may provide a second Encoding to have the data transcoded as it is read. For example,

    encoding: 'UTF-32BE:UTF-8'

    would read UTF-32BE data from the file but transcode it to UTF-8 before parsing.


These examples assume prior execution of:

string = "foo,0\nbar,1\nbaz,2\n"
path = 't.csv'
File.write(path, string)

With no block given, returns a new CSV object.

Create a CSV object using a file path:

csv = CSV.open(path)
csv # => #<CSV io_type:File io_path:"t.csv" encoding:UTF-8 lineno:0 col_sep:"," row_sep:"\n" quote_char:"\"">

Create a CSV object using an open File:

csv = CSV.open(File.open(path))
csv # => #<CSV io_type:File io_path:"t.csv" encoding:UTF-8 lineno:0 col_sep:"," row_sep:"\n" quote_char:"\"">

With a block given, calls the block with the created CSV object; returns the block's return value:

Using a file path:

csv = CSV.open(path) {|csv| p csv}
csv # => #<CSV io_type:File io_path:"t.csv" encoding:UTF-8 lineno:0 col_sep:"," row_sep:"\n" quote_char:"\"">

Output:

#<CSV io_type:File io_path:"t.csv" encoding:UTF-8 lineno:0 col_sep:"," row_sep:"\n" quote_char:"\"">

Using an open File:

csv = CSV.open(File.open(path)) {|csv| p csv}
csv # => #<CSV io_type:File io_path:"t.csv" encoding:UTF-8 lineno:0 col_sep:"," row_sep:"\n" quote_char:"\"">

Output:

#<CSV io_type:File io_path:"t.csv" encoding:UTF-8 lineno:0 col_sep:"," row_sep:"\n" quote_char:"\"">

Raises an exception if the argument is not a String object or IO object:

# Raises TypeError (no implicit conversion of Symbol into String)
CSV.open(:foo)
[ GitHub ]

  
# File 'lib/csv.rb', line 1412

def open(filename, mode="r", **options)
  # wrap a File opened with the remaining args with no newline
  # decorator
  file_opts = {universal_newline: false}.merge(options)
  options.delete(:invalid)
  options.delete(:undef)
  options.delete(:replace)

  begin
    f = File.open(filename, mode, **file_opts)
  rescue ArgumentError => e
    raise unless /needs binmode/.match?(e.message) and mode == "r"
    mode = "rb"
    file_opts = {encoding: Encoding.default_external}.merge(file_opts)
    retry
  end
  begin
    csv = new(f, **options)
  rescue Exception
    f.close
    raise
  end

  # handle blocks like Ruby's open(), not like the CSV library
  if block_given?
    begin
      yield csv
    ensure
      csv.close
    end
  else
    csv
  end
end

.parse(string) ⇒ array_of_arrays .parse(io) ⇒ array_of_arrays .parse(string, headers: ..., **options) ⇒ CSV .parse(io, headers: ..., **options) ⇒ CSV .parse(string, **options) {|row| ... } .parse(io, **options) {|row| ... }

Parses string or io using the specified options.

  • Argument string should be a String object; it will be put into a new StringIO object positioned at the beginning.

Without Option #headers

Without option #headers case.

These examples assume prior execution of:

string = "foo,0\nbar,1\nbaz,2\n"
path = 't.csv'
File.write(path, string)

With no block given, returns an Array of Arrays formed from the source.

Parse a String:

a_of_a = CSV.parse(string)
a_of_a # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

Parse an open File:

a_of_a = File.open(path) do |file|
  CSV.parse(file)
end
a_of_a # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

With a block given, calls the block with each parsed row:

Parse a String:

CSV.parse(string) {|row| p row }

Output:

["foo", "0"]
["bar", "1"]
["baz", "2"]

Parse an open File:

File.open(path) do |file|
  CSV.parse(file) {|row| p row }
end

Output:

["foo", "0"]
["bar", "1"]
["baz", "2"]
With Option #headers

With option #headers case.

These examples assume prior execution of:

string = "Name,Count\nfoo,0\nbar,1\nbaz,2\n"
path = 't.csv'
File.write(path, string)

With no block given, returns a ::CSV::Table object formed from the source.

Parse a String:

csv_table = CSV.parse(string, headers: ['Name', 'Count'])
csv_table # => #<CSV::Table mode:col_or_row row_count:5>

Parse an open File:

csv_table = File.open(path) do |file|
  CSV.parse(file, headers: ['Name', 'Count'])
end
csv_table # => #<CSV::Table mode:col_or_row row_count:4>

With a block given, calls the block with each parsed row, which has been formed into a ::CSV::Row object:

Parse a String:

CSV.parse(string, headers: ['Name', 'Count']) {|row| p row }

Output:

# <CSV::Row "Name":"foo" "Count":"0">
# <CSV::Row "Name":"bar" "Count":"1">
# <CSV::Row "Name":"baz" "Count":"2">

Parse an open File:

File.open(path) do |file|
  CSV.parse(file, headers: ['Name', 'Count']) {|row| p row }
end

Output:

# <CSV::Row "Name":"foo" "Count":"0">
# <CSV::Row "Name":"bar" "Count":"1">
# <CSV::Row "Name":"baz" "Count":"2">

Raises an exception if the argument is not a String object or IO object:

# Raises NoMethodError (undefined method `close' for :foo:Symbol)
CSV.parse(:foo)
[ GitHub ]

  
# File 'lib/csv.rb', line 1559

def parse(str, **options, &block)
  csv = new(str, **options)

  return csv.each(&block) if block_given?

  # slurp contents, if no block is given
  begin
    csv.read
  ensure
    csv.close
  end
end

.parse_line(string) ⇒ Array? .parse_line(io) ⇒ Array? .parse_line(string, **options) ⇒ Array? .parse_line(io, **options) ⇒ Array? .parse_line(string, headers: true, **options) ⇒ CSV? .parse_line(io, headers: true, **options) ⇒ CSV?

Returns the data created by parsing the first line of string or io using the specified options.

  • Argument string should be a String object; it will be put into a new StringIO object positioned at the beginning.

Without Option #headers

Without option #headers, returns the first row as a new Array.

These examples assume prior execution of:

string = "foo,0\nbar,1\nbaz,2\n"
path = 't.csv'
File.write(path, string)

Parse the first line from a String object:

CSV.parse_line(string) # => ["foo", "0"]

Parse the first line from a File object:

File.open(path) do |file|
  CSV.parse_line(file) # => ["foo", "0"]
end # => ["foo", "0"]

Returns nil if the argument is an empty String:

CSV.parse_line('') # => nil
With Option #headers

With option #headers, returns the first row as a ::CSV::Row object.

These examples assume prior execution of:

string = "Name,Count\nfoo,0\nbar,1\nbaz,2\n"
path = 't.csv'
File.write(path, string)

Parse the first line from a String object:

CSV.parse_line(string, headers: true) # => #<CSV::Row "Name":"foo" "Count":"0">

Parse the first line from a File object:

File.open(path) do |file|
  CSV.parse_line(file, headers: true)
end # => #<CSV::Row "Name":"foo" "Count":"0">

Raises an exception if the argument is nil:

# Raises ArgumentError (Cannot parse nil as CSV):
CSV.parse_line(nil)
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# File 'lib/csv.rb', line 1632

def parse_line(line, **options)
  new(line, **options).each.first
end

.read(source, **options) ⇒ array_of_arrays .read(source, headers: true, **options) ⇒ CSV

Opens the given source with the given options (see .open), reads the source (see #read), and returns the result, which will be either an Array of Arrays or a ::CSV::Table.

Without headers:

string = "foo,0\nbar,1\nbaz,2\n"
path = 't.csv'
File.write(path, string)
CSV.read(path) # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

With headers:

string = "Name,Value\nfoo,0\nbar,1\nbaz,2\n"
path = 't.csv'
File.write(path, string)
CSV.read(path, headers: true) # => #<CSV::Table mode:col_or_row row_count:4>
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# File 'lib/csv.rb', line 1656

def read(path, **options)
  open(path, **options) { |csv| csv.read }
end

.readlines(source, **options)

Alias for .read.

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# File 'lib/csv.rb', line 1664

def readlines(path, **options)
  read(path, **options)
end

.table(source, **options)

Calls .read with source, options, and certain default options:

Returns a ::CSV::Table object.

Example:

string = "Name,Value\nfoo,0\nbar,1\nbaz,2\n"
path = 't.csv'
File.write(path, string)
CSV.table(path) # => #<CSV::Table mode:col_or_row row_count:4>
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# File 'lib/csv.rb', line 1683

def table(path, **options)
  default_options = {
    headers:           true,
    converters:        :numeric,
    header_converters: :symbol,
  }
  options = default_options.merge(options)
  read(path, **options)
end

Instance Attribute Details

#binmode?Boolean (readonly)

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# File 'lib/csv.rb', line 2051

def binmode?
  if @io.respond_to?(:binmode?)
    @io.binmode?
  else
    false
  end
end

#encodingendcoding (readonly)

Returns the encoding used for parsing and generating; see Character Encodings (M17n or Multilingualization):

CSV.new('').encoding # => #<Encoding:UTF-8>
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# File 'lib/csv.rb', line 1982

attr_reader :encoding

#eof (readonly)

Alias for #eof?.

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# File 'lib/csv.rb', line 2099

alias_method :eof, :eof?

#force_quotes?Boolean (readonly)

Returns the value that determines whether all output fields are to be quoted; used for generating; see Option force_quotes:

CSV.new('').force_quotes? # => false
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# File 'lib/csv.rb', line 1962

def force_quotes?
  @writer_options[:force_quotes]
end

#header_row?Boolean (readonly)

Returns true if the next row to be read is a header row; false otherwise.

Without headers:

string = "foo,0\nbar,1\nbaz,2\n"
csv = CSV.new(string)
csv.header_row? # => false

With headers:

string = "Name,Value\nfoo,0\nbar,1\nbaz,2\n"
csv = CSV.new(string, headers: true)
csv.header_row? # => true
csv.shift # => #<CSV::Row "Name":"foo" "Value":"0">
csv.header_row? # => false

Raises an exception if the source is not opened for reading:

string = "foo,0\nbar,1\nbaz,2\n"
csv = CSV.new(string)
csv.close
# Raises IOError (not opened for reading)
csv.header_row?
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# File 'lib/csv.rb', line 2415

def header_row?
  parser.header_row?
end

#liberal_parsing?Boolean (readonly)

Returns the value that determines whether illegal input is to be handled; used for parsing; see Option liberal_parsing:

CSV.new('').liberal_parsing? # => false
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# File 'lib/csv.rb', line 1972

def liberal_parsing?
  parser.liberal_parsing?
end

#return_headers?Boolean (readonly)

Returns the value that determines whether headers are to be returned; used for parsing; see Option return_headers:

CSV.new('').return_headers? # => false
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# File 'lib/csv.rb', line 1918

def return_headers?
  parser.return_headers?
end

#skip_blanks?Boolean (readonly)

Returns the value that determines whether blank lines are to be ignored; used for parsing; see Option skip_blanks:

CSV.new('').skip_blanks? # => false
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# File 'lib/csv.rb', line 1951

def skip_blanks?
  parser.skip_blanks?
end

#unconverted_fields?Boolean (readonly)

Returns the value that determines whether unconverted fields are to be available; used for parsing; see Option unconverted_fields:

CSV.new('').unconverted_fields? # => nil
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# File 'lib/csv.rb', line 1890

def unconverted_fields?
  parser.unconverted_fields?
end

#write_headers?Boolean (readonly)

Returns the value that determines whether headers are to be written; used for generating; see Option write_headers:

CSV.new('').write_headers? # => nil
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# File 'lib/csv.rb', line 1928

def write_headers?
  @writer_options[:write_headers]
end

Instance Method Details

#<<(row) ⇒ self Also known as: #add_row, #puts

Appends a row to self.

  • Argument row must be an Array object or a ::CSV::Row object.

  • The output stream must be open for writing.


Append Arrays:

CSV.generate do |csv|
  csv << ['foo', 0]
  csv << ['bar', 1]
  csv << ['baz', 2]
end # => "foo,0\nbar,1\nbaz,2\n"

Append CSV::Rows:

headers = []
CSV.generate do |csv|
  csv << CSV::Row.new(headers, ['foo', 0])
  csv << CSV::Row.new(headers, ['bar', 1])
  csv << CSV::Row.new(headers, ['baz', 2])
end # => "foo,0\nbar,1\nbaz,2\n"

Headers in ::CSV::Row objects are not appended:

headers = ['Name', 'Count']
CSV.generate do |csv|
  csv << CSV::Row.new(headers, ['foo', 0])
  csv << CSV::Row.new(headers, ['bar', 1])
  csv << CSV::Row.new(headers, ['baz', 2])
end # => "foo,0\nbar,1\nbaz,2\n"

Raises an exception if row is not an Array or CSV::Row:

CSV.generate do |csv|
  # Raises NoMethodError (undefined method `collect' for :foo:Symbol)
  csv << :foo
end

Raises an exception if the output stream is not opened for writing:

path = 't.csv'
File.write(path, '')
File.open(path) do |file|
  CSV.open(file) do |csv|
    # Raises IOError (not opened for writing)
    csv << ['foo', 0]
  end
end
[ GitHub ]

  
# File 'lib/csv.rb', line 2162

def <<(row)
  writer << row
  self
end

#add_row(row)

Alias for #<<.

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# File 'lib/csv.rb', line 2166

alias_method :add_row, :<<

#build_fields_converter(initial_converters, options) (private)

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# File 'lib/csv.rb', line 2606

def build_fields_converter(initial_converters, options)
  fields_converter = FieldsConverter.new(options)
  normalize_converters(initial_converters).each do |name, converter|
    fields_converter.add_converter(name, &converter)
  end
  fields_converter
end

#build_header_fields_converter (private)

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# File 'lib/csv.rb', line 2588

def build_header_fields_converter
  specific_options = {
    builtin_converters: HeaderConverters,
    accept_nil: true,
  }
  options = @base_fields_converter_options.merge(specific_options)
  build_fields_converter(@initial_header_converters, options)
end

#build_parser_fields_converter (private)

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# File 'lib/csv.rb', line 2576

def build_parser_fields_converter
  specific_options = {
    builtin_converters: Converters,
  }
  options = @base_fields_converter_options.merge(specific_options)
  build_fields_converter(@initial_converters, options)
end

#build_writer_fields_converter (private)

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# File 'lib/csv.rb', line 2601

def build_writer_fields_converter
  build_fields_converter(@initial_write_converters,
                         @write_fields_converter_options)
end

#col_sepString

Returns the encoded column separator; used for parsing and writing; see Option col_sep:

CSV.new('').col_sep # => ","
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# File 'lib/csv.rb', line 1821

def col_sep
  parser.column_separator
end

#convert(converter_name) ⇒ array_of_procs #convert {|field, field_info| ... } ⇒ array_of_procs

  • With no block, installs a field converter (a Proc).

  • With a block, defines and installs a custom field converter.

  • Returns the Array of installed field converters.

  • Argument converter_name, if given, should be the name of an existing field converter.

See Field Converters.


With no block, installs a field converter:

csv = CSV.new('')
csv.convert(:integer)
csv.convert(:float)
csv.convert(:date)
csv.converters # => [:integer, :float, :date]

The block, if given, is called for each field:

  • Argument field is the field value.

  • Argument field_info is a ::CSV::FieldInfo object containing details about the field.

The examples here assume the prior execution of:

string = "foo,0\nbar,1\nbaz,2\n"
path = 't.csv'
File.write(path, string)

Example giving a block:

csv = CSV.open(path)
csv.convert {|field, field_info| p [field, field_info]; field.upcase }
csv.read # => [["FOO", "0"], ["BAR", "1"], ["BAZ", "2"]]

Output:

["foo", #<struct CSV::FieldInfo index=0, line=1, header=nil>]
["0", #<struct CSV::FieldInfo index=1, line=1, header=nil>]
["bar", #<struct CSV::FieldInfo index=0, line=2, header=nil>]
["1", #<struct CSV::FieldInfo index=1, line=2, header=nil>]
["baz", #<struct CSV::FieldInfo index=0, line=3, header=nil>]
["2", #<struct CSV::FieldInfo index=1, line=3, header=nil>]

The block need not return a String object:

csv = CSV.open(path)
csv.convert {|field, field_info| field.to_sym }
csv.read # => [[:foo, :"0"], [:bar, :"1"], [:baz, :"2"]]

If converter_name is given, the block is not called:

csv = CSV.open(path)
csv.convert(:integer) {|field, field_info| fail 'Cannot happen' }
csv.read # => [["foo", 0], ["bar", 1], ["baz", 2]]

Raises a parse-time exception if converter_name is not the name of a built-in field converter:

csv = CSV.open(path)
csv.convert(:nosuch) => [nil]
# Raises NoMethodError (undefined method `arity' for nil:NilClass)
csv.read
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# File 'lib/csv.rb', line 2233

def convert(name = nil, &converter)
  parser_fields_converter.add_converter(name, &converter)
end

#convert_fields(fields, headers = false) (private)

Processes fields with @converters, or @header_converters if #headers is passed as true, returning the converted field set. Any converter that changes the field into something other than a ::String halts the pipeline of conversion for that field. This is primarily an efficiency shortcut.

[ GitHub ]

  
# File 'lib/csv.rb', line 2551

def convert_fields(fields, headers = false)
  if headers
    header_fields_converter.convert(fields, nil, 0)
  else
    parser_fields_converter.convert(fields, @headers, lineno)
  end
end

#convertersArray

Returns an Array containing field converters; see Field Converters:

csv = CSV.new('')
csv.converters # => []
csv.convert(:integer)
csv.converters # => [:integer]
csv.convert(proc {|x| x.to_s })
csv.converters
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# File 'lib/csv.rb', line 1876

def converters
  parser_fields_converter.map do |converter|
    name = Converters.rassoc(converter)
    name ? name.first : converter
  end
end

#determine_encoding(encoding, internal_encoding) (private)

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# File 'lib/csv.rb', line 2514

def determine_encoding(encoding, internal_encoding)
  # honor the IO encoding if we can, otherwise default to ASCII-8BIT
  io_encoding = raw_encoding
  return io_encoding if io_encoding

  return Encoding.find(internal_encoding) if internal_encoding

  if encoding
    encoding, = encoding.split(":", 2) if encoding.is_a?(String)
    return Encoding.find(encoding)
  end

  Encoding.default_internal || Encoding.default_external
end

#eachEnumerator #each {|row| ... }

Calls the block with each successive row. The data source must be opened for reading.

Without headers:

string = "foo,0\nbar,1\nbaz,2\n"
csv = CSV.new(string)
csv.each do |row|
  p row
end

Output:

["foo", "0"]
["bar", "1"]
["baz", "2"]

With headers:

string = "Name,Value\nfoo,0\nbar,1\nbaz,2\n"
csv = CSV.new(string, headers: true)
csv.each do |row|
  p row
end

Output:

<CSV::Row "Name":"foo" "Value":"0">
<CSV::Row "Name":"bar" "Value":"1">
<CSV::Row "Name":"baz" "Value":"2">

Raises an exception if the source is not opened for reading:

string = "foo,0\nbar,1\nbaz,2\n"
csv = CSV.new(string)
csv.close
# Raises IOError (not opened for reading)
csv.each do |row|
  p row
end
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# File 'lib/csv.rb', line 2344

def each(&block)
  parser_enumerator.each(&block)
end

#eof?Boolean (readonly) Also known as: #eof

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# File 'lib/csv.rb', line 2087

def eof?
  return false if @eof_error
  begin
    parser_enumerator.peek
    false
  rescue MalformedCSVError => error
    @eof_error = error
    false
  rescue StopIteration
    true
  end
end

#field_size_limitInteger?

Returns the limit for field size; used for parsing; see Option field_size_limit:

CSV.new('').field_size_limit # => nil
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# File 'lib/csv.rb', line 1851

def field_size_limit
  parser.field_size_limit
end

#flock(*args)

Raises:

  • (NotImplementedError)
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# File 'lib/csv.rb', line 2059

def flock(*args)
  raise NotImplementedError unless @io.respond_to?(:flock)
  @io.flock(*args)
end

#gets

Alias for #shift.

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# File 'lib/csv.rb', line 2463

alias_method :gets,     :shift

#header_convert(name = nil, &converter)

The block need not return a String object:

csv = CSV.open(path, headers: true)
csv.header_convert {|header, field_info| header.to_sym }
table = csv.read
table.headers # => [:Name, :Value]

If converter_name is given, the block is not called:

csv = CSV.open(path, headers: true)
csv.header_convert(:downcase) {|header, field_info| fail 'Cannot happen' }
table = csv.read
table.headers # => ["name", "value"]

Raises a parse-time exception if converter_name is not the name of a built-in field converter:

csv = CSV.open(path, headers: true)
csv.header_convert(:nosuch)
# Raises NoMethodError (undefined method `arity' for nil:NilClass)
csv.read
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# File 'lib/csv.rb', line 2299

def header_convert(name = nil, &converter)
  header_fields_converter.add_converter(name, &converter)
end

#header_convertersArray

Returns an Array containing header converters; used for parsing; see Header Converters:

CSV.new('').header_converters # => []
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# File 'lib/csv.rb', line 1938

def header_converters
  header_fields_converter.map do |converter|
    name = HeaderConverters.rassoc(converter)
    name ? name.first : converter
  end
end

#header_fields_converter (private)

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# File 'lib/csv.rb', line 2584

def header_fields_converter
  @header_fields_converter ||= build_header_fields_converter
end

#headersObject

Returns the value that determines whether headers are used; used for parsing; see Option headers:

CSV.new('').headers # => nil
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# File 'lib/csv.rb', line 1900

def headers
  if @writer
    @writer.headers
  else
    parsed_headers = parser.headers
    return parsed_headers if parsed_headers
    raw_headers = @parser_options[:headers]
    raw_headers = nil if raw_headers == false
    raw_headers
  end
end

#inspectString

Returns a String showing certain properties of self:

string = "Name,Value\nfoo,0\nbar,1\nbaz,2\n"
csv = CSV.new(string, headers: true)
s = csv.inspect
s # => "#<CSV io_type:StringIO encoding:UTF-8 lineno:0 col_sep:\",\" row_sep:\"\\n\" quote_char:\"\\\"\" headers:true>"
[ GitHub ]

  
# File 'lib/csv.rb', line 2474

def inspect
  str = ["#<", self.class.to_s, " io_type:"]
  # show type of wrapped IO
  if    @io == $stdout then str << "$stdout"
  elsif @io == $stdin  then str << "$stdin"
  elsif @io == $stderr then str << "$stderr"
  else                      str << @io.class.to_s
  end
  # show IO.path(), if available
  if @io.respond_to?(:path) and (p = @io.path)
    str << " io_path:" << p.inspect
  end
  # show encoding
  str << " encoding:" << @encoding.name
  # show other attributes
  ["lineno", "col_sep", "row_sep", "quote_char"].each do |attr_name|
    if a = __send__(attr_name)
      str << " " << attr_name << ":" << a.inspect
    end
  end
  ["skip_blanks", "liberal_parsing"].each do |attr_name|
    if a = __send__("#{attr_name}?")
      str << " " << attr_name << ":" << a.inspect
    end
  end
  _headers = headers
  str << " headers:" << _headers.inspect if _headers
  str << ">"
  begin
    str.join('')
  rescue  # any encoding error
    str.map do |s|
      e = Encoding::Converter.asciicompat_encoding(s.encoding)
      e ? s.encode(e) : s.force_encoding("ASCII-8BIT")
    end.join('')
  end
end

#ioctl(*args)

Raises:

  • (NotImplementedError)
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# File 'lib/csv.rb', line 2064

def ioctl(*args)
  raise NotImplementedError unless @io.respond_to?(:ioctl)
  @io.ioctl(*args)
end

#lineArray

Returns the line most recently read:

string = "foo,0\nbar,1\nbaz,2\n"
path = 't.csv'
File.write(path, string)
CSV.open(path) do |csv|
  csv.each do |row|
    p [csv.lineno, csv.line]
  end
end

Output:

[1, "foo,0\n"]
[2, "bar,1\n"]
[3, "baz,2\n"]
[ GitHub ]

  
# File 'lib/csv.rb', line 2037

def line
  parser.line
end

#line_noInteger

Returns the count of the rows parsed or generated.

Parsing:

string = "foo,0\nbar,1\nbaz,2\n"
path = 't.csv'
File.write(path, string)
CSV.open(path) do |csv|
  csv.each do |row|
    p [csv.lineno, row]
  end
end

Output:

[1, ["foo", "0"]]
[2, ["bar", "1"]]
[3, ["baz", "2"]]

Generating:

CSV.generate do |csv|
  p csv.lineno; csv << ['foo', 0]
  p csv.lineno; csv << ['bar', 1]
  p csv.lineno; csv << ['baz', 2]
end

Output:

0
1
2
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# File 'lib/csv.rb', line 2013

def lineno
  if @writer
    @writer.lineno
  else
    parser.lineno
  end
end

#normalize_converters(converters) (private)

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# File 'lib/csv.rb', line 2529

def normalize_converters(converters)
  converters ||= []
  unless converters.is_a?(Array)
    converters = [converters]
  end
  converters.collect do |converter|
    case converter
    when Proc # custom code block
      [nil, converter]
    else # by name
      [converter, nil]
    end
  end
end

#parser (private)

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# File 'lib/csv.rb', line 2614

def parser
  @parser ||= Parser.new(@io, parser_options)
end

#parser_enumerator (private)

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# File 'lib/csv.rb', line 2623

def parser_enumerator
  @parser_enumerator ||= parser.parse
end

#parser_fields_converter (private)

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# File 'lib/csv.rb', line 2572

def parser_fields_converter
  @parser_fields_converter ||= build_parser_fields_converter
end

#parser_options (private)

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# File 'lib/csv.rb', line 2618

def parser_options
  @parser_options.merge(header_fields_converter: header_fields_converter,
                        fields_converter: parser_fields_converter)
end

#path

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# File 'lib/csv.rb', line 2069

def path
  @io.path if @io.respond_to?(:path)
end

#puts(row)

Alias for #<<.

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# File 'lib/csv.rb', line 2167

alias_method :puts,    :<<

#quote_charcharacter

Returns the encoded quote character; used for parsing and writing; see Option quote_char:

CSV.new('').quote_char # => "\""
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# File 'lib/csv.rb', line 1841

def quote_char
  parser.quote_character
end

#raw_encoding (private)

Returns the encoding of the internal IO object.

[ GitHub ]

  
# File 'lib/csv.rb', line 2562

def raw_encoding
  if @io.respond_to? :internal_encoding
    @io.internal_encoding || @io.external_encoding
  elsif @io.respond_to? :encoding
    @io.encoding
  else
    nil
  end
end

#readArray, CSV Also known as: #readlines

Forms the remaining rows from self into:

  • A ::CSV::Table object, if headers are in use.

  • An Array of Arrays, otherwise.

The data source must be opened for reading.

Without headers:

string = "foo,0\nbar,1\nbaz,2\n"
path = 't.csv'
File.write(path, string)
csv = CSV.open(path)
csv.read # => [["foo", "0"], ["bar", "1"], ["baz", "2"]]

With headers:

string = "Name,Value\nfoo,0\nbar,1\nbaz,2\n"
path = 't.csv'
File.write(path, string)
csv = CSV.open(path, headers: true)
csv.read # => #<CSV::Table mode:col_or_row row_count:4>

Raises an exception if the source is not opened for reading:

string = "foo,0\nbar,1\nbaz,2\n"
csv = CSV.new(string)
csv.close
# Raises IOError (not opened for reading)
csv.read
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# File 'lib/csv.rb', line 2379

def read
  rows = to_a
  if parser.use_headers?
    Table.new(rows, headers: parser.headers)
  else
    rows
  end
end

#readline

Alias for #shift.

[ GitHub ]

  
# File 'lib/csv.rb', line 2464

alias_method :readline, :shift

#readlines

Alias for #read.

[ GitHub ]

  
# File 'lib/csv.rb', line 2387

alias_method :readlines, :read

#rewind

Rewinds the underlying IO object and resets CSV's lineno() counter.

[ GitHub ]

  
# File 'lib/csv.rb', line 2102

def rewind
  @parser = nil
  @parser_enumerator = nil
  @eof_error = nil
  @writer.rewind if @writer
  @io.rewind
end

#row_sepString

Returns the encoded row separator; used for parsing and writing; see Option row_sep:

CSV.new('').row_sep # => "\n"
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# File 'lib/csv.rb', line 1831

def row_sep
  parser.row_separator
end

#shiftArray, ... Also known as: #gets, #readline

Returns the next row of data as:

  • An Array if no headers are used.

  • A ::CSV::Row object if headers are used.

The data source must be opened for reading.

Without headers:

string = "foo,0\nbar,1\nbaz,2\n"
csv = CSV.new(string)
csv.shift # => ["foo", "0"]
csv.shift # => ["bar", "1"]
csv.shift # => ["baz", "2"]
csv.shift # => nil

With headers:

string = "Name,Value\nfoo,0\nbar,1\nbaz,2\n"
csv = CSV.new(string, headers: true)
csv.shift # => #<CSV::Row "Name":"foo" "Value":"0">
csv.shift # => #<CSV::Row "Name":"bar" "Value":"1">
csv.shift # => #<CSV::Row "Name":"baz" "Value":"2">
csv.shift # => nil

Raises an exception if the source is not opened for reading:

string = "foo,0\nbar,1\nbaz,2\n"
csv = CSV.new(string)
csv.close
# Raises IOError (not opened for reading)
csv.shift
[ GitHub ]

  
# File 'lib/csv.rb', line 2452

def shift
  if @eof_error
    eof_error, @eof_error = @eof_error, nil
    raise eof_error
  end
  begin
    parser_enumerator.next
  rescue StopIteration
    nil
  end
end

#skip_linesRegexp?

Returns the Regexp used to identify comment lines; used for parsing; see Option skip_lines:

CSV.new('').skip_lines # => nil
[ GitHub ]

  
# File 'lib/csv.rb', line 1861

def skip_lines
  parser.skip_lines
end

#stat(*args)

Raises:

  • (NotImplementedError)
[ GitHub ]

  
# File 'lib/csv.rb', line 2073

def stat(*args)
  raise NotImplementedError unless @io.respond_to?(:stat)
  @io.stat(*args)
end

#to_i

Raises:

  • (NotImplementedError)
[ GitHub ]

  
# File 'lib/csv.rb', line 2078

def to_i
  raise NotImplementedError unless @io.respond_to?(:to_i)
  @io.to_i
end

#to_io

[ GitHub ]

  
# File 'lib/csv.rb', line 2083

def to_io
  @io.respond_to?(:to_io) ? @io.to_io : @io
end

#writer (private)

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# File 'lib/csv.rb', line 2627

def writer
  @writer ||= Writer.new(@io, writer_options)
end

#writer_fields_converter (private)

[ GitHub ]

  
# File 'lib/csv.rb', line 2597

def writer_fields_converter
  @writer_fields_converter ||= build_writer_fields_converter
end

#writer_options (private)

[ GitHub ]

  
# File 'lib/csv.rb', line 2631

def writer_options
  @writer_options.merge(header_fields_converter: header_fields_converter,
                        fields_converter: writer_fields_converter)
end