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

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

The basic syntax of the function is:

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

This 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, that sub‑array is merged until no deeper arrays remain.

Below is an example demonstrating its usage:

$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 output of the above code is:

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

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

)

As shown, the keys in $array2 recursively overwrite the corresponding keys in $array1, while other keys remain unchanged, making the function convenient for merging 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 want to keep existing keys and values in the target array while adding new ones from the source, you can use array_merge_recursive(). This function behaves similarly but does not overwrite existing keys and values like array_replace_recursive() does.

In summary, array_replace_recursive() is a very useful function that recursively merges two or more arrays, allowing you to control whether keys and values are overwritten or retained, and is worth using when you need to combine PHP arrays.