class CSV
inherits Reference

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.

Constants

DEFAULT_QUOTE_CHAR = '"'

DEFAULT_SEPARATOR = ','

Class methods

.build(separator : Char = DEFAULT_SEPARATOR, quote_char : Char = DEFAULT_QUOTE_CHAR, quoting : Builder::Quoting = Builder::Quoting::RFC, &) : String

Builds a CSV. This yields a CSV::Builder to the given block.

Takes optional quoting argument to define quote behavior.

require "csv"

result = CSV.build do |csv|
  csv.row "one", "two"
  csv.row "three"
end
result # => "one,two\nthree\n"
result = CSV.build(quoting: CSV::Builder::Quoting::ALL) do |csv|
  csv.row "one", "two"
  csv.row "three"
end
result # => "\"one\",\"two\"\n\"three\"\n"

See: CSV::Builder::Quoting

View source

.build(io : IO, separator : Char = DEFAULT_SEPARATOR, quote_char : Char = DEFAULT_QUOTE_CHAR, quoting : Builder::Quoting = Builder::Quoting::RFC, &) : Nil

Appends CSV data to the given IO. This yields a CSV::Builder that writes to the given IO.

require "csv"

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"

View source

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

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

See CSV.parse about the separator and quote_char arguments.

require "csv"

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

Output:

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

View source

.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.

See CSV.parse about the separator and quote_char arguments.

require "csv"

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

View source

.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.

Takes optional separator and quote_char arguments for defining non-standard csv cell separators and quote characters.

require "csv"

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

View source

.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.

• If strip is true, row values are stripped with String#strip before being returned from methods.
• If headers is true, row values can be accessed with header names or patterns. Headers are always stripped.

See CSV.parse about the separator and quote_char arguments.

View source

.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, and yields it to the given block once for each row in the CSV.

• If strip is true, row values are stripped with String#strip before being returned from methods.
• If headers is true, row values can be accessed with header names or patterns. Headers are always stripped.

See CSV.parse about the separator and quote_char arguments.

View source

Methods

#[](header : String) : String

Returns the current row's value corresponding to the given header name. Raises KeyError if no such header exists. Raises CSV::Error if headers were not requested.

View source

#[](column : Int) : String

Returns the current row's value at the given column index. A negative index counts from the end. Raises IndexError if no such column exists.

View source

#[](header_pattern : Regex) : String

Returns the current row's value corresponding to the given header_pattern. Raises KeyError if no such header exists. Raises CSV::Error if headers were not requested.

View source

#[]?(header : String) : String?

Returns the current row's value corresponding to the given header name. Returns nil if no such header exists. Raises CSV::Error if headers were not requested.

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#[]?(column : Int) : String?

Returns the current row's value at the given column index. A negative index counts from the end. Returns nil if no such column exists.

View source

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

Returns the current row's value corresponding to the given header_pattern. Returns nil if no such header exists. Raises CSV::Error if headers were not requested.

View source

#each(&) : Nil

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

View source

#headers : Array(String)

Returns this CSV headers. Their values are always stripped. Raises CSV::Error if headers were not requested.

View source

#next

Advanced the cursor to the next row. Must be called once to position the cursor in the first row. Returns true if a next row was found, false otherwise.

View source

#rewind

Rewinds this CSV to the beginning, rewinding the underlying IO if any.

View source

#row : Row

Returns the current row as a Row instance.

View source

#values_at(*columns : Int)

Returns a tuple of the current row's values at given indices A negative index counts from the end. Raises IndexError if any column doesn't exist The behavior of returning a tuple is similar to Hash#values_at

View source

#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. Raises CSV::Error if headers were not requested The behavior of returning a tuple is similar to Hash#values_at

View source