Using PHP's array_replace_recursive() Function to Recursively Merge Arrays

PHP is a popular web programming language with a rich function library; the array_replace_recursive() function merges one or more arrays recursively, combining their keys, values, and sub‑arrays.

The basic syntax is:

array_replace_recursive(array1, array2, array3 ...);

The function accepts multiple arrays as arguments and returns a merged array. It recursively compares keys and values; when keys match, their values are merged recursively, and if a value is itself an array, the merge continues until no sub‑arrays remain.

Example:

$array1 = array(
    'fruit' => array(
        'apple' => 1,
        'orange' => 4,
        'banana' => 3
    ),
    'vegetable' => array(
        'potato' => 2,
        'broccoli' => 1,
        'carrot' => 4
    )
);

$array2 = array(
    'fruit' => array(
        'orange' => 2
    ),
    'vegetable' => array(
        'potato' => 3,
        'broccoli' => 2,
        'carrot' => 1
    )
);

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

The resulting output is:

Array
(
    [fruit] => Array
        (
            [apple] => 1
            [orange] => 2
            [banana] => 3
        )

    [vegetable] => Array
        (
            [potato] => 3
            [broccoli] => 2
            [carrot] => 1
        )
)

The output shows that $array2 recursively overwrote the corresponding keys of $array1, while other keys remained unchanged, demonstrating how the function can conveniently merge arrays.

Note that when the same key appears in multiple arrays, later arrays overwrite earlier ones, and array keys must be strings or integers; otherwise a warning is generated.

If you prefer to keep existing keys in the target array and only add missing keys from the source, you can use array_merge_recursive(), which behaves similarly but does not overwrite existing values.

In summary, array_replace_recursive() is a practical function for recursively merging arrays in PHP, allowing you to control whether keys and values are overwritten or retained during the merge.

The article also provides links to download learning materials for Java, C, front‑end development, C++, and PHP.