PHP array_merge Function

last modified March 13, 2025

The PHP array_merge function combines two or more arrays into a single array. It's essential for array manipulation in PHP applications.

Basic Definition

The array_merge function merges elements of multiple arrays into one array. Values from later arrays overwrite earlier ones for matching keys.

Syntax: array_merge(array ...$arrays): array. It accepts one or more arrays as parameters. String keys are overwritten, numeric keys are reindexed.

Basic array_merge Example

This demonstrates merging two simple arrays with string keys.

basic_array_merge.php

<?php

$array1 = ["color" => "red", 2, 4];
$array2 = ["a", "b", "color" => "green", "shape" => "circle", 4];

$result = array_merge($array1, $array2);
print_r($result);

This merges two arrays with both string and numeric keys. The "color" value from $array2 overwrites $array1's value. Numeric keys are reindexed.

Merging Numeric Keys

When merging arrays with numeric keys, values are appended and keys renumbered.

numeric_keys.php

<?php

$numbers1 = [10, 20, 30];
$numbers2 = [40, 50, 60];

$merged = array_merge($numbers1, $numbers2);
print_r($merged);

The output shows all elements combined with new numeric indices (0-5). Unlike string keys, numeric keys don't cause overwrites but get reindexed.

Merging Multiple Arrays

array_merge can combine more than two arrays in a single call.

multiple_arrays.php

<?php

$user = ["name" => "John"];
$profile = ["age" => 30, "city" => "New York"];
$preferences = ["theme" => "dark", "notifications" => true];

$account = array_merge($user, $profile, $preferences);
print_r($account);

This combines three associative arrays into one. All string keys remain distinct, so no values are overwritten in this example.

Merging With Duplicate String Keys

When string keys collide, later array values overwrite earlier ones.

duplicate_keys.php

<?php

$config1 = ["debug" => false, "log_level" => "warning"];
$config2 = ["debug" => true, "timeout" => 30];

$finalConfig = array_merge($config1, $config2);
print_r($finalConfig);

The "debug" value from $config2 overwrites $config1's value. Other keys merge normally. This behavior is useful for configuration overrides.

Merging Indexed and Associative Arrays

array_merge handles mixed key types appropriately.

mixed_arrays.php

<?php

$indexed = ["apple", "banana"];
$associative = ["fruit" => "orange", "vegetable" => "carrot"];

$combined = array_merge($indexed, $associative);
print_r($combined);

Numeric keys are reindexed (0,1), while string keys remain unchanged. The result contains all elements from both arrays in sequence.

Best Practices

Key Conflicts: Be aware of overwrite behavior with string keys.
Performance: For large arrays, consider memory implications.
Type Safety: Ensure merged arrays have compatible value types.
Alternatives: Use + operator for different merge behavior.

Source

PHP array_merge Documentation

This tutorial covered the PHP array_merge function with practical examples showing various merging scenarios and behaviors.

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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