How to Split Large PHP Arrays with array_chunk – A Step‑by‑Step Guide

In PHP development, dividing a large array into smaller chunks is a common need, and the array_chunk() function provides a straightforward solution.

Function Syntax

array array_chunk ( array $array , int $size [, bool $preserve_keys = false ] )

The function accepts three parameters: $array – the input array to be split. $size – the desired size of each chunk. $preserve_keys – optional boolean indicating whether to retain the original keys in the resulting chunks (default false).

Basic Example (no key preservation)

<?php
$array = array('a','b','c','d','e','f','g','h','i','j');
$chunks = array_chunk($array, 3);
print_r($chunks);
?>

The above code splits a 10‑element array into chunks of three, producing four sub‑arrays (the last containing a single element). The output is:

Array
(
    [0] => Array
        (
            [0] => a
            [1] => b
            [2] => c
        )

    [1] => Array
        (
            [0] => d
            [1] => e
            [2] => f
        )

    [2] => Array
        (
            [0] => g
            [1] => h
            [2] => i
        )

    [3] => Array
        (
            [0] => j
        )
)

Preserving Original Keys

By setting the third argument $preserve_keys to true, the original keys are kept in each chunk.

<?php
$array = array('a' => 1, 'b' => 2, 'c' => 3, 'd' => 4, 'e' => 5, 'f' => 6);
$chunks = array_chunk($array, 2, true);
print_r($chunks);
?>

This produces three chunks, each retaining the associative keys:

Array
(
    [0] => Array
        (
            [a] => 1
            [b] => 2
        )

    [1] => Array
        (
            [c] => 3
            [d] => 4
        )

    [2] => Array
        (
            [e] => 5
            [f] => 6
        )
)

Conclusion

The array_chunk() function is a practical tool for PHP developers, enabling easy division of large arrays into manageable pieces while optionally preserving original keys, which simplifies handling of extensive data sets in backend applications.