Request for Comments: array_column

• Version: 2.4
• Date: 2013-01-11
• Author: Ben Ramsey ramsey@php.net
• Status: Implemented in PHP 5.5
• First Published at: http://wiki.php.net/rfc/array_column

This RFC proposes a new array function that returns the values of the specified column from a multi-dimensional array. Inspired by database methods like PDOStatement::fetchColumn(), array_column() moves useful functionality into the core that once had to be implemented in userland code with sometimes complex loops.

This has been submitted as a pull request on GitHub, where there has already been a significant amount of discussion.

array array_column(array $input, mixed $columnKey[, mixed $indexKey])

array_column() returns the values from a single column of the input array, identified by the columnKey. Optionally, you may provide an indexKey to index the values in the returned array by the values from the indexKey column in the input array.

input

A multi-dimensional array (record set) from which to pull a column of values.

columnKey

The column of values to return. This value may be the integer key of the column you wish to retrieve, or it may be the string key name for an associative array.

indexKey

(Optional.) The column to use as the index/keys for the returned array. This value may be the integer key of the column, or it may be the string key name.

Returns an array of values representing a single column from the input array.

<?php
// Array representing a possible record set returned from a database
$records = array(
    array(
        'id' => 2135,
        'first_name' => 'John',
        'last_name' => 'Doe'
    ),
    array(
        'id' => 3245,
        'first_name' => 'Sally',
        'last_name' => 'Smith'
    ),
    array(
        'id' => 5342,
        'first_name' => 'Jane',
        'last_name' => 'Jones'
    ),
    array(
        'id' => 5623,
        'first_name' => 'Peter',
        'last_name' => 'Doe'
    )
);
 
$firstNames = array_column($records, 'first_name');
print_r($firstNames);

The above example will output:

Array
(
    [0] => John
    [1] => Sally
    [2] => Jane
    [3] => Peter
)

<?php
$records = array(
    array(1, 'John', 'Doe'),
    array(2, 'Sally', 'Smith'),
    array(3, 'Jane', 'Jones')
);
 
$lastNames = array_column($records, 2);
print_r($lastNames);

The above example will output:

Array
(
    [0] => Doe
    [1] => Smith
    [2] => Jones
)

<?php
// Using the $records array from Example #1
$lastNames = array_column($records, 'last_name', 'id');
print_r($lastNames);

The above example will output:

Array
(
    [2135] => Doe
    [3245] => Smith
    [5342] => Jones
    [5623] => Doe
)

With array_column() the relationship in finding the values of columnKey to indexKey is much like that of a SQL left join. All values of the columnKey are returned. When a corresponding indexKey cannot be found, the value will be keyed with an integer, starting from zero.

The following examples will all use the same $mismatchedColumns array defined here:

<?php
$mismatchedColumns = array(
    array(
        'a' => 'foo',
        'b' => 'bar',
        'e' => 'baz'
    ),
    array(
        'a' => 'qux',
        'c' => 'quux',
        'd' => 'corge'
    ),
    array(
        'a' => 'grault',
        'b' => 'garply',
        'e' => 'waldo'
    ),
);

In this example, all rows contain an “a” key, but only two contain a “b” key. If we want to retrieve all “a” values and key them by “b” values, then array_column() behaves like this:

<?php
$foo = array_column($mismatchedColumns, 'a', 'b');
$bar = array('bar' => 'foo', 'qux', 'garply' => 'grault');
 
/*
Both $foo and $bar contain values that look like this:
 
Array
(
    [bar] => foo
    [0] => qux
    [garply] => grault
)
*/

However, if we want to retrieve all “b” values and key them by “a” values, we will only have two elements in the resulting array, since only two rows contain “b” values.

// There is a corresponding "a" value for each "b" value
print_r(array_column($mismatchedColumns, 'b', 'a'));
 
/*
Array
(
    [foo] => bar
    [grault] => garply
)
*/
 
// There are no corresponding "c" values for either "b" value
print_r(array_column($mismatchedColumns, 'b', 'c'));
 
/*
Array
(
    [0] => bar
    [1] => garply
)
*/

In the event that more than one row contains the same value for indexKey, then the last columnKey value for that indexKey will overwrite the previous value.

// Using the $records array from Example #1
$firstNames = array_column($records, 'first_name', 'last_name');
print_r($firstNames);
 
/*
Array
(
    [Doe] => Peter
    [Smith] => Sally
    [Jones] => Jane
)
*/

The patch (including tests) for this proposal is available in GitHub Pull Request #257.

The mailing list discussion is available here.

Voting ends not before Friday, January 18, 2013. The PHP language is not changed, so a 50% + 1 majority is required.

Accept array_column() for inclusion in PHP?
Real name	Yes	No
ab
aharvey
arpad
ashnazg
blanchonvincent
cataphract
chx
davey
derick
fa
frozenfire
googleguy
guilhermeblanco
gwynne
hradtke
ifeghali
juliens
jwage
kalle
kriscraig
levim
lstrojny
marco
mfonda
mike
mj
nikic
oaass
pajoye
patrickallaert
peehaa
pollita
ralphschindler
rasmus
rdohms
remi
salathe
seld
shiflett
stas
treffynnon
tyrael
willfitch
zeev
Final result:	38	6
This poll has been closed.

• 1.0 (2012-06-21): Initial draft, following discussion on on GitHub Pull Request #56
• 2.0 (2013-01-11): Updated to reflect mailing list and pull request feedback.
• 2.1 (2013-01-11): Adding link to new pull request: https://github.com/php/php-src/pull/257
• 2.2 (2013-01-11): Opened voting
• 2.3 (2013-01-12): Updates to the RFC (new examples, etc.), based on mailing list feedback
• 2.4 (2013-01-14): Removed array_pluck() alias