class CSV

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:

csv.cr
csv/error.cr

Constant Summary

DEFAULT_QUOTE_CHAR = '"'
DEFAULT_SEPARATOR = ','

Constructors

Class Method Summary

Instance Method Summary

Instance methods inherited from class Reference

==(other : self)
==(other)
==
, dup dup, hash(hasher) hash, inspect(io : IO) : Nil inspect, object_id : UInt64 object_id, pretty_print(pp) : Nil pretty_print, same?(other : Reference)
same?(other : Nil)
same?
, to_s(io : IO) : Nil to_s

Constructor methods inherited from class Reference

new new

Instance methods inherited from class Object

!=(other) !=, !~(other) !~, ==(other) ==, ===(other : JSON::Any)
===(other : YAML::Any)
===(other)
===
, =~(other) =~, class class, dup dup, hash(hasher)
hash
hash
, inspect(io : IO)
inspect
inspect
, itself itself, not_nil! not_nil!, pretty_inspect(width = 79, newline = "\n", indent = 0) : String pretty_inspect, pretty_print(pp : PrettyPrint) : Nil pretty_print, tap(&block) tap, to_json(io : IO)
to_json
to_json
, to_pretty_json(indent : String = " ")
to_pretty_json(io : IO, indent : String = " ")
to_pretty_json
, to_s
to_s(io : IO)
to_s
, to_yaml(io : IO)
to_yaml
to_yaml
, try(&block) try, unsafe_as(type : T.class) forall T unsafe_as

Constructor methods inherited from class Object

from_json(string_or_io, root : String) : self
from_json(string_or_io) : self
from_json
, from_yaml(string_or_io) : self from_yaml

Constructor Detail

def self.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]
def self.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.

  • 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]

Class Method Detail

def self.build(io : IO, &block) #

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

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"

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def self.build(&block) : String #

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

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

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def self.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).

See CSV.parse about the separator and quote_char arguments.

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

Output:

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

[View source]
def self.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.

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

[View source]
def self.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.

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

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Instance Method Detail

def [](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.


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def [](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.


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def [](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.


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def []?(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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def []?(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.


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def []?(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.


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def each(&block) : Nil #

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


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def headers : Array(String) #

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


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def 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.


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def row : Row #

Returns the current row as a Row instance.


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def 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


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def 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]