📖 PHP array_merge_recursive() Function — Explained

The array_merge_recursive() function in PHP is used to merge two or more arrays recursively. It helps you combine values under the same keys without overwriting any data.

Unlike array_merge(), which replaces duplicate keys, this function keeps both values by converting them into arrays.

🔑 Keyword Focus: php array_merge_recursive preserve numeric keys

If you're trying to preserve numeric keys while merging arrays in PHP, it's important to know that array_merge_recursive() will reindex numeric keys by default. Let’s see what that means.

📌 Syntax

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

Parameters:

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

Returns:

• New merged array.
• String keys: merged into arrays.
• Numeric keys: reindexed and appended.

📌 Example 1: Simple Merge Without Conflicting Keys

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

Output:

Array ( [color] => Array ( [0] => red [1] => green ) [0] => 2 [1] => 4 [2] => a [3] => b [shape] => circle )

Explanation: "color" exists in both arrays, so its values are combined. Numeric keys are reindexed sequentially.

📌 Example 2: Nested Array Merge

$array1 = array("details" => array("name" => "John", "age" => 25)); $array2 = array("details" => array("city" => "Karachi")); $result = array_merge_recursive($array1, $array2);

Output:

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

Explanation: Since the "details" key contains arrays in both, they are merged recursively into one array.

📌 Example 3: Conflicting Keys (String and Numeric)

$array1 = array("fruit" => "apple", 0 => "orange"); $array2 = array("fruit" => "banana", 0 => "grape"); $result = array_merge_recursive($array1, $array2);

Output:

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

Note: Numeric keys like 0 are not preserved. They are renumbered.

📦 Use Cases

• Merging form data from different sources
• Combining multiple config files
• Joining nested arrays from API responses

⚠️ Important Notes

• Recursively merges arrays at all levels
• Can cause deep nesting if keys repeat
• Numeric keys are not preserved — use $array1 + $array2 if needed

📌 Conclusion

array_merge_recursive() is great for merging arrays deeply without losing values. But if you're concerned about numeric key preservation, this function may not be ideal.

For preserving numeric keys, use the + operator or build a custom function that suits your logic.

📘 Official PHP Docs

Visit PHP Manual

💡 Keyword Recap:

• php array_merge_recursive preserve numeric keys
• php merge arrays without overwriting
• php array merge nested