PHP array_merge_recursive() Function — Explained

📖 PHP array_merge_recursive() Function — Explained

The array_merge_recursive() function in PHP is used to merge two or more arrays.
Unlike array_merge(), which replaces the values of duplicate keys, array_merge_recursive() combines values with the same keys into an array.

---

📌 Syntax:

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

Parameters:

• $array1, $array2, ... → Arrays you want to merge.

Returns:

• A new merged array. If two arrays have the same string keys, their values will be merged into an array instead of being overwritten.

---

📖 How It Works:

• If keys are different: Values are simply added to the result.

• If keys are the same:

  • If the key is a string → The values are merged into an array.

  • If the key is numeric → The values are appended.

---

📌 Example 1: Simple Merge Without Conflicting Keys

<?php
$array1 = array("color" => "red", 2, 4);
$array2 = array("a", "b", "color" => "green", "shape" => "circle");

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

print_r($result);
?>

✅ Output:

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

    [0] => 2
    [1] => 4
    [2] => a
    [3] => b
    [shape] => circle
)

Explanation:

• The key "color" exists in both arrays, so their values ("red" and "green") are combined into an array.

• Numeric keys are appended sequentially.

---

📌 Example 2: Nested Array Merge

<?php
$array1 = array("details" => array("name" => "John", "age" => 25));
$array2 = array("details" => array("city" => "Karachi"));

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

print_r($result);
?>

✅ Output:

Array
(
    [details] => Array
        (
            [name] => John
            [age] => 25
            [city] => Karachi
        )
)

Explanation:

• The "details" key exists in both arrays. Since their values are arrays themselves, array_merge_recursive() merges them.

---

📌 Example 3: Conflicting Keys (String and Numeric)

<?php
$array1 = array("fruit" => "apple", 0 => "orange");
$array2 = array("fruit" => "banana", 0 => "grape");

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

print_r($result);
?>

✅ Output:

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

    [0] => orange
    [1] => grape
)

---

📌 Use Cases:

• Combining form inputs from multiple sources.

• Merging configuration arrays without losing values.

• Combining nested data structures (e.g., merging API responses).

---

📌 Important Notes:

• It recursively merges arrays. If values are arrays themselves, it will continue to merge them at deeper levels.

• Be cautious: It can result in deeply nested structures if arrays have the same keys at multiple levels.

• If you don’t want this recursive merging behavior, use array_merge() instead.

---

📌 Conclusion:

array_merge_recursive() is a powerful function when working with complex or nested arrays, where you want to preserve all values, including those under the same keys, by combining them into arrays instead of overwriting.

---

📌 Official PHP Docs:

👉 https://www.php.net/manual/en/function.array-merge-recursive.php