class CSV

• CSV
• Reference
• Object

Overview

Provides methods and classes for parsing and generating CSV (comma-separated values) strings.

This module conforms to RFC 4180.

Parsing

Several ways of parsing CSV are provided. The most straight-forward, but slow or inefficient for some scenarios, is CSV#parse, which returns an array of arrays of all data.

Rows can be traversed in a linear fashion with CSV#each_row, or using an Iterator.

To parse a CSV in an efficient way, optionally being able to access row values from header names, create an instance of a CSV.

Parsing with CSV#new

A CSV instance holds a cursor to the current row in the CSV. The cursor is advanced by invoking #next, which returns true if a next row was found, and false otherwise. A first call to #next is required to position the csv parser in the first row.

Once positioned in a row, values can be obtained with the several #[] methods, which can accept a header name, column position, or header name pattern as a Regex.

Additionally, a Row object can be obtained with the #row method which provides similar methods and can be converted to an Array or Hash.

Example

require "csv"

csv = CSV.new("Name, Age\nJohn, 20\nPeter, 30", headers: true)
csv.next # => true

csv["Name"]  # => "John"
csv[0]       # => "John"
csv[-2]      # => "John"
csv[/name/i] # => "John"

csv["Age"] # => " 20"

csv.row.to_a # => ["John", " 20"]
csv.row.to_h # => {"Name" => "John", "Age" => " 20"}

csv.next    # => true
csv["Name"] # => "Peter"

csv.next # => false

Building

To create CSV data, check CSV#build and the CSV::Builder class.

Defined in:

Constant Summary

DEFAULT_QUOTE_CHAR = '"'

DEFAULT_SEPARATOR = ','

Constructors

• .new(string_or_io : String | IO, headers = false, strip = false, separator : Char = DEFAULT_SEPARATOR, quote_char : Char = DEFAULT_QUOTE_CHAR)

  Creates a new instance from the given String or IO.

• .new(string_or_io : String | IO, headers = false, strip = false, separator : Char = DEFAULT_SEPARATOR, quote_char : Char = DEFAULT_QUOTE_CHAR, &block)

  Creates a new instance from the given String or IO, and yields it to the given block once for each row in the CSV.

Class Method Summary

• .build(io : IO, &block)

  Appends CSV data to the given IO.

• .build(&block) : String

  Builds a CSV.

• .each_row(string_or_io : String | IO, separator : Char = DEFAULT_SEPARATOR, quote_char : Char = DEFAULT_QUOTE_CHAR, &block)

  Yields each of a CSV's rows as an Array(String).

• .each_row(string_or_io : String | IO, separator : Char = DEFAULT_SEPARATOR, quote_char : Char = DEFAULT_QUOTE_CHAR)

  Returns an Iterator of Array(String) over a CSV's rows.

• .parse(string_or_io : String | IO, separator : Char = DEFAULT_SEPARATOR, quote_char : Char = DEFAULT_QUOTE_CHAR) : Array(Array(String))

  Parses a CSV or IO into an array.

Instance Method Summary

• #[](header : String) : String

  Returns the current row's value corresponding to the given header name.

• #[](column : Int) : String

  Returns the current row's value at the given column index.

• #[](header_pattern : Regex) : String

  Returns the current row's value corresponding to the given header_pattern.

• #[]?(header : String) : String?

  Returns the current row's value corresponding to the given header name.

• #[]?(column : Int) : String?

  Returns the current row's value at the given column index.

• #[]?(header_pattern : Regex) : String?

  Returns the current row's value corresponding to the given header_pattern.

• #each(&block) : Nil

  Invokes the block once for each row in this CSV, yielding self.

• #headers : Array(String)

  Returns this CSV headers.

• #next

  Advanced the cursor to the next row.

• #row : Row

  Returns the current row as a Row instance.

• #values_at(*columns : Int)

  Returns a tuple of the current row's values at given indices A negative index counts from the end.

• #values_at(*headers : String)

  Returns a tuple of the current row's values corresponding to the given headers Raises KeyError if any header doesn't exist.

Constructor Detail

Class Method Detail

io = IO::Memory.new
io.puts "HEADER"
CSV.build(io) do |csv|
  csv.row "one", "two"
  csv.row "three"
end
io.to_s # => "HEADER\none,two\nthree\n"

result = CSV.build do |csv|
  csv.row "one", "two"
  csv.row "three"
end
result # => "one,two\nthree\n"

CSV.each_row("one,two\nthree") do |row|
  puts row
end

["one", "two"]
["three"]

rows = CSV.each_row("one,two\nthree")
rows.next # => ["one", "two"]
rows.next # => ["three"]

CSV.parse("one,two\nthree")
# => [["one", "two"], ["three"]]
CSV.parse("one;two\n'three;'", separator: ';', quote_char: '\'')
# => [["one", "two"], ["three;"]]

Instance Method Detail