PHP array_merge_recursive: Merge Arrays Deeply

PHP array_merge_recursive joins two or more arrays into one nested array and keeps all values with their keys.

Syntax of array_merge_recursive in PHP

The array_merge_recursive function adds values from one array into another and forms nested arrays for repeated keys.

Here is the syntax:

array_merge_recursive(array $array1, array $array2, array ...$arrays): array

This function takes each key from the arrays and groups their values together into one combined array with nested arrays.

Here is a quick example:

$array1 = ["a" => "red", "b" => "blue"];
$array2 = ["a" => "green", "c" => "yellow"];
$result = array_merge_recursive($array1, $array2);
print_r($result);

This example shows that the function puts both values under the same key and creates a nested array for that key.

Here is the output:

Array
(
    [a] => Array
        (
            [0] => red
            [1] => green
        )

    [b] => blue
    [c] => yellow
)

Nested Arrays Merging with array_merge_recursive in PHP

When both arrays have the same key, this function places all values under that key and forms nested arrays automatically.

For example:

$array1 = ["colors" => ["red", "blue"]];
$array2 = ["colors" => ["green", "yellow"]];
$result = array_merge_recursive($array1, $array2);
print_r($result);

The output:

Array
(
    [colors] => Array
        (
            [0] => red
            [1] => blue
            [2] => green
            [3] => yellow
        )

)

This example shows that PHP joins inner arrays under the same key and returns a new array that holds all values.

The Difference Between array_merge and array_merge_recursive

array_merge replaces values of matching keys with new ones, while array_merge_recursive groups all values under the same key.

Use array_merge when you want the last value to replace the previous value. Use array_merge_recursive when you want all values together.

Examples of array_merge_recursive in PHP

Combine two arrays with the same keys:

$array1 = ["fruit" => "apple"];
$array2 = ["fruit" => "banana"];
$result = array_merge_recursive($array1, $array2);
print_r($result);

This example shows how the function groups both values under one key and gives you a nested array with all values.

The output:

Array
(
    [fruit] => Array
        (
            [0] => apple
            [1] => banana
        )

)

Combine multiple arrays with different keys:

$array1 = ["a" => 1];
$array2 = ["b" => 2];
$array3 = ["a" => 3, "c" => 4];
$result = array_merge_recursive($array1, $array2, $array3);
print_r($result);

This example shows how PHP combines values from many arrays into one and puts them under each key without loss of any data.

The output:

Array
(
    [a] => Array
        (
            [0] => 1
            [1] => 3
        )

    [b] => 2
    [c] => 4
)

Combine arrays with inner arrays:

$array1 = ["data" => ["x" => 10]];
$array2 = ["data" => ["y" => 20]];
$result = array_merge_recursive($array1, $array2);
print_r($result);

This example shows how the function joins inner arrays and keeps all nested values under the same key without overwriting.

The output:

Array
(
    [data] => Array
        (
            [x] => 10
            [y] => 20
        )

)

Combine arrays of different depths:

$array1 = ["config" => ["db" => ["host" => "localhost"]]];
$array2 = ["config" => ["db" => ["port" => 3306]]];
$result = array_merge_recursive($array1, $array2);
print_r($result);

This example shows how PHP handles arrays with deep levels and returns a nested array with all the information kept intact.

The output:

Array
(
    [config] => Array
        (
            [db] => Array
                (
                    [host] => localhost
                    [port] => 3306
                )

        )

)

Wrapping Up

You learned what array_merge_recursive does and how it groups values from arrays under one key.

Here is a quick recap:

• array_merge replaces values with new ones, and array_merge_recursive groups all values under one key to form nested arrays.

FAQs

$array1 = array("a" => "red", "b" => "green");
$array2 = array("a" => "blue", "c" => "yellow");

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

Array
(
    [a] => Array
        (
            [0] => red
            [1] => blue
        )

    [b] => green
    [c] => yellow
)

$a = array("x" => "one");
$b = array("x" => "two");

print_r(array_merge($a, $b));
print_r(array_merge_recursive($a, $b));

array_merge:
Array
(
    [x] => two
)

array_merge_recursive:
Array
(
    [x] => Array
        (
            [0] => one
            [1] => two
        )
)

$arr1 = array("id" => 1);
$arr2 = array("id" => 2, "name" => "John");
$arr3 = array("city" => "London");

$result = array_merge_recursive($arr1, $arr2, $arr3);
print_r($result);

Array
(
    [id] => Array
        (
            [0] => 1
            [1] => 2
        )

    [name] => John
    [city] => London
)

$a = array("color" => "red");
$b = array("color" => "blue");

print_r(array_merge_recursive($a, $b));
print_r(array_replace_recursive($a, $b));

array_merge_recursive:
Array
(
    [color] => Array
        (
            [0] => red
            [1] => blue
        )
)

array_replace_recursive:
Array
(
    [color] => blue
)

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