PHP array_reverse Function

last modified March 13, 2025

The PHP array_reverse function returns an array with elements in reverse order. It's useful for processing arrays from end to start.

Basic Definition

The array_reverse function reverses the order of array elements. It can preserve or reset numeric keys based on the second parameter.

Syntax: array_reverse(array $array, bool $preserve_keys = false): array. When $preserve_keys is true, numeric keys are preserved in the reversed array.

Basic array_reverse Example

This demonstrates simple array reversal with default parameters.

basic_array_reverse.php

<?php

$numbers = [1, 2, 3, 4, 5];
$reversed = array_reverse($numbers);

print_r($reversed);

The example reverses a simple numeric array. Note that new numeric keys are assigned starting from 0 in the reversed array by default.

Preserving Array Keys

This shows how to maintain original numeric keys when reversing an array.

preserve_keys.php

<?php

$colors = [
    10 => 'red',
    20 => 'green',
    30 => 'blue'
];
$reversed = array_reverse($colors, true);

print_r($reversed);

With true as the second parameter, the original numeric keys are preserved in the reversed array. This is useful for associative arrays.

Reversing Associative Arrays

Demonstrates how string keys are always preserved in reversed arrays.

associative_array.php

<?php

$user = [
    'name' => 'John',
    'age' => 30,
    'city' => 'New York'
];
$reversed = array_reverse($user);

print_r($reversed);

String keys in associative arrays are always preserved regardless of the second parameter. The order of elements is reversed while keeping keys.

Multidimensional Array Reversal

Shows how array_reverse affects only the top level of multidimensional arrays.

multidimensional_array.php

<?php

$matrix = [
    [1, 2, 3],
    [4, 5, 6],
    [7, 8, 9]
];
$reversed = array_reverse($matrix);

print_r($reversed);

Only the outer array is reversed while inner arrays maintain their order. To reverse inner arrays, you would need to apply array_reverse recursively.

Practical Use Case

Demonstrates a real-world scenario where array_reverse might be useful.

practical_use.php

<?php

$logEntries = [
    '2023-01-01' => 'System started',
    '2023-01-02' => 'User logged in',
    '2023-01-03' => 'Data processed',
    '2023-01-04' => 'System shutdown'
];

// Display log entries in reverse chronological order
$reversedLogs = array_reverse($logEntries, true);

foreach ($reversedLogs as $date => $entry) {
    echo "$date: $entry\n";
}

This example shows how to display log entries in reverse chronological order. The date keys are preserved to maintain the association between dates and events.

Best Practices

Key Preservation: Use true for $preserve_keys when key-value pairs matter.
Performance: Consider memory usage with very large arrays.
Multidimensional Arrays: Remember it only affects the first level.
Readability: Document why you're reversing an array when it's not obvious.

Source

PHP array_reverse Documentation

This tutorial covered the PHP array_reverse function with practical examples showing its usage for various array manipulation 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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