PHP array_chunk Function

last modified March 13, 2025

The PHP array_chunk function splits an array into chunks of smaller arrays. It's useful for processing large arrays in manageable parts.

Basic Definition

The array_chunk function divides an array into chunks of specified size. It returns a new multidimensional array containing the chunks.

Syntax: array_chunk(array $array, int $size, bool $preserve_keys = false): array. The $size determines chunk size. $preserve_keys keeps original keys.

Basic array_chunk Example

This demonstrates splitting a simple array into chunks of 2 elements each.

basic_array_chunk.php

<?php

$numbers = [1, 2, 3, 4, 5, 6, 7, 8];
$chunks = array_chunk($numbers, 2);

print_r($chunks);

Output shows the original array divided into 4 chunks, each containing 2 elements. The keys are reindexed starting from 0 in each chunk.

Preserving Original Keys

This example shows how to maintain original array keys in the chunks.

preserve_keys.php

<?php

$assocArray = [
    'a' => 1,
    'b' => 2,
    'c' => 3,
    'd' => 4
];
$chunks = array_chunk($assocArray, 2, true);

print_r($chunks);

With preserve_keys set to true, the output maintains 'a', 'b', 'c', 'd' keys in their respective chunks instead of reindexing.

Uneven Chunk Division

When array length isn't divisible by chunk size, the last chunk will be smaller.

uneven_chunks.php

<?php

$colors = ['red', 'green', 'blue', 'yellow', 'black'];
$chunks = array_chunk($colors, 2);

print_r($chunks);

This creates 3 chunks: two with 2 colors each and a final chunk with 1 color. The function handles uneven divisions automatically.

Processing Large Arrays

Chunking is useful for processing large arrays in batches to manage memory.

batch_processing.php

<?php

$bigArray = range(1, 1000);
$batchSize = 100;

foreach (array_chunk($bigArray, $batchSize) as $chunk) {
    // Process 100 elements at a time
    processBatch($chunk);
}

function processBatch(array $batch): void {
    echo "Processing " . count($batch) . " elements\n";
}

This processes 1000 elements in batches of 100, reducing memory usage by not loading all elements at once. Each iteration handles one chunk.

Multidimensional Array Chunking

Chunking works with multidimensional arrays, splitting at the top level.

multidimensional.php

<?php

$matrix = [
    [1, 2, 3],
    [4, 5, 6],
    [7, 8, 9],
    [10, 11, 12]
];
$chunks = array_chunk($matrix, 2);

print_r($chunks);

The 4x3 matrix is split into two chunks, each containing 2 sub-arrays. The inner arrays remain intact within their respective chunks.

Best Practices

Memory Management: Use chunking for large datasets to reduce memory load.
Batch Processing: Process chunks sequentially for better performance.
Key Preservation: Preserve keys when original indexes matter.
Chunk Size: Choose appropriate sizes based on system resources.

Source

PHP array_chunk Documentation

This tutorial covered the PHP array_chunk function with practical examples showing its usage for array processing scenarios.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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