How to Use array_chunk in PHP: Syntax and Examples

Use array_chunk(array $array, int $size, bool $preserve_keys = false) to split an array into smaller arrays each with a maximum of $size elements. It returns a multidimensional array with chunks. Set $preserve_keys to true to keep original keys.

Syntax

The array_chunk function splits an array into smaller arrays (chunks) of a specified size.

• $array: The input array to split.
• $size: The maximum number of elements in each chunk.
• $preserve_keys (optional): If true, original keys are preserved; otherwise, keys are reindexed starting from 0.

php

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

Example

This example shows how to split an array of numbers into chunks of 3 elements each. It also demonstrates preserving keys.

php

<?php
$input = ["a" => 1, "b" => 2, "c" => 3, "d" => 4, "e" => 5];

// Split into chunks of 3 without preserving keys
$chunks = array_chunk($input, 3);
print_r($chunks);

// Split into chunks of 3 preserving keys
$chunks_preserved = array_chunk($input, 3, true);
print_r($chunks_preserved);
?>

Output

Array
(
    [0] => Array
        (
            [0] => 1
            [1] => 2
            [2] => 3
        )

    [1] => Array
        (
            [0] => 4
            [1] => 5
        )
)
Array
(
    [0] => Array
        (
            [a] => 1
            [b] => 2
            [c] => 3
        )

    [1] => Array
        (
            [d] => 4
            [e] => 5
        )
)

Common Pitfalls

Common mistakes when using array_chunk include:

• Forgetting that keys are reindexed by default, which can cause issues if keys matter.
• Setting chunk size to zero or negative, which causes a warning and returns false.
• Expecting the function to modify the original array (it returns a new array instead).

php

<?php
// Wrong: chunk size zero causes warning and returns false
$result = @array_chunk([1,2,3], 0);
var_dump($result); // bool(false)

// Right: use positive chunk size
$result = array_chunk([1,2,3], 2);
print_r($result);
?>

Output

Warning: array_chunk(): Size parameter expected to be greater than 0 in ...
bool(false)
Array
(
    [0] => Array
        (
            [0] => 1
            [1] => 2
        )

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

Quick Reference

Parameter	Description	Default
$array	Input array to split	Required
$size	Maximum elements per chunk	Required
$preserve_keys	Keep original keys if true	false

Key Takeaways

Use array_chunk to split arrays into smaller arrays of a fixed size.

By default, keys are reindexed; set preserve_keys to true to keep original keys.

Chunk size must be a positive integer to avoid warnings.

array_chunk returns a new array and does not modify the original.

Useful for processing large arrays in smaller parts.