# Introducing array_column() in PHP 5.5


By Ben Ramsey

Published on March 20, 2013


Earlier today, [David Soria Parra][dsp] declared a [feature freeze on PHP 5.5][freeze] and [tagged php-5.5.0beta1][php-5.5.0beta1], but not before merging in [pull request #257][pr257], which includes my humble addition to the PHP programming language: `array_column()`.

The story of `array_column()` begins at PHP Tek in 2008. As I recall, it was [Spooons][] who suggested it to me. It is functionality that nearly every developer has to implement in user-land code at some point in their careers, so I felt it only natural that it be built into the language, so I did just that.

My original patch for `array_column()` was written for PHP 5.2, but it sat around collecting dust for many years, until April of last year, when [PHP moved to git and GitHub][git]. That's when it became easy enough to apply the patch and send a pull request, which I did. It wasn't quite that simple, though, since I had to follow the [official PHP project RFC process][rfc-process], but it wasn't a pain either.

My goal for `array_column()` was simplicity. Many implement the functionality in different ways, and many call the function by other names (such as "pluck"), but I wanted to keep it simple and recognizable. It follows this function signature:

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

Given a multi-dimensional array of data, `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.

For example, using the following array of data, we tell `array_column()` to return an array of just the last names, indexed by their record IDs.

```php
$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'
    )
);

$lastNames = array_column($records, 'last_name', 'id');
```

If we call `print_r()` on `$lastNames`, you'll see a resulting array that looks a bit like this:

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

And that's all there is to it. I hope you find my little addition to the PHP language helpful. I had a lot of fun writing it, and following the PHP RFC process was a great learning experience.

[dsp]: https://web.archive.org/web/20130318132622/http://blog.experimentalworks.net/
[freeze]: https://twitter.com/dsp_/status/314021877565755393
[php-5.5.0beta1]: https://github.com/php/php-src/tree/php-5.5.0beta1
[pr257]: https://github.com/php/php-src/pull/257
[spooons]: https://twitter.com/spooons
[git]: https://www.php.net/archive/2012.php#id2012-03-20-1
[rfc-process]: https://web.archive.org/web/20131211093419/http://blogs.oracle.com/opal/entry/the_mysterious_php_rfc_process