# 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.

NOTE To use `CSV` or its children, you must explicitly import it with `require "csv"`

###
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

- .new(string_or_io : String | IO, headers : Bool = false, strip : Bool = 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, &)

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

  Builds a CSV.

- .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`.

- .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)`.

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

  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, *, options : Regex::MatchOptions = Regex::MatchOptions::None) : String

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

- #[]?(header : String) : String | Nil

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

- #[]?(column : Int) : String | Nil

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

- #[]?(header_pattern : Regex, *, options : Regex::MatchOptions = Regex::MatchOptions::None) : String | Nil

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

- #each(&) : Nil

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

- #headers : Array(String)

  Returns this CSV headers.

- #next : Bool

  Advanced the cursor to the next row.

- #rewind : Nil

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

- #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.

### Instance methods inherited from class `Reference`

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

### Constructor methods inherited from class `Reference`

new new, unsafe_construct(address : Pointer, *args, **opts) : self unsafe_construct

### Class methods inherited from class `Reference`

pre_initialize(address : Pointer) pre_initialize

### Instance methods inherited from class `Object`

! : Bool !, !=(other) !=, !~(other) !~, ==(other) ==, ===(other : JSON::Any)
===(other : YAML::Any)
===(other) ===, =~(other) =~, as(type : Class) as, as?(type : Class) as?, class class, dup dup, hash(hasher)
hash hash, in?(collection : Object) : Bool
in?(*values : Object) : Bool in?, inspect(io : IO) : Nil
inspect : String inspect, is_a?(type : Class) : Bool is_a?, itself itself, nil? : Bool nil?, not_nil!(message)
not_nil! not_nil!, pretty_inspect(width = 79, newline = "\n", indent = 0) : String pretty_inspect, pretty_print(pp : PrettyPrint) : Nil pretty_print, responds_to?(name : Symbol) : Bool responds_to?, tap(&) tap, to_json(io : IO) : Nil
to_json : String to_json, to_pretty_json(indent : String = " ") : String
to_pretty_json(io : IO, indent : String = " ") : Nil to_pretty_json, to_s(io : IO) : Nil
to_s : String to_s, to_yaml(io : IO) : Nil
to_yaml : String to_yaml, try(&) try, unsafe_as(type : T.class) forall T unsafe_as

### Class methods inherited from class `Object`

from_json(string_or_io, root : String)
from_json(string_or_io) from_json, from_yaml(string_or_io : String | IO) from_yaml

### Macros inherited from class `Object`

class_getter(*names, &block) class_getter, class_getter!(*names) class_getter!, class_getter?(*names, &block) class_getter?, class_property(*names, &block) class_property, class_property!(*names) class_property!, class_property?(*names, &block) class_property?, class_setter(*names) class_setter, def_clone def_clone, def_equals(*fields) def_equals, def_equals_and_hash(*fields) def_equals_and_hash, def_hash(*fields) def_hash, delegate(*methods, to object) delegate, forward_missing_to(delegate) forward_missing_to, getter(*names, &block) getter, getter!(*names) getter!, getter?(*names, &block) getter?, property(*names, &block) property, property!(*names) property!, property?(*names, &block) property?, setter(*names) setter

##
Constructor Detail

def self.new(string_or_io : String | IO, headers : Bool = false, strip : Bool = 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.

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`, 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.

##
Class Method Detail

def self.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`

def self.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"

def self.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"]

def self.each_row(string_or_io : String | IO, separator : Char = DEFAULT_SEPARATOR, quote_char : Char = DEFAULT_QUOTE_CHAR) : Iterator(Array(String)) #

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"]

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.

    require "csv"

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

##
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.

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.

def [](header_pattern : Regex, *, options : Regex::MatchOptions = Regex::MatchOptions::None) : 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.

def []?(header : String) : String | Nil #

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.

def []?(column : Int) : String | Nil #

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.

def []?(header_pattern : Regex, *, options : Regex::MatchOptions = Regex::MatchOptions::None) : String | Nil #

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.

def each(&) : Nil #

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

def headers : Array(String) #

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

def next : Bool #

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.

def rewind : Nil #

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

def row : Row #

Returns the current row as a `Row` instance.

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`

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`