Master PHP’s array_replace_recursive: Recursive Array Merging Made Easy

PHP is a popular web programming language with a rich function library. The array_replace_recursive() function merges one array with one or more other arrays recursively, including their key‑value pairs and subarrays. This article introduces its usage.

The basic syntax is:

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

The function accepts multiple arrays as parameters and returns the merged array. Arrays are merged recursively, meaning keys and values are compared recursively. If two keys match, their values are merged recursively. If a value is an array, it is merged recursively until no subarrays remain.

Below is an 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 output is as follows:

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

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

$array2 recursively overwrites the corresponding keys of $array1, while other keys remain unaffected, making array merging more convenient.

When using array_replace_recursive(), if the same key appears in multiple arrays, later arrays overwrite earlier ones. 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 keys/values from the source array that do not exist, you can use array_merge_recursive(). This function is similar, but array_replace_recursive() overwrites existing keys and values.

In summary, array_replace_recursive() is a very useful function. It can recursively merge two or more arrays and overwrite or retain existing keys and values as desired. When you need to merge PHP arrays, this function is worth using.