Merge two arrays keeping original keys in PHP

In PHP, you can merge two arrays while preserving their original keys using the array union operator (+). This operator combines arrays by keeping all unique keys from both arrays, with values from the left array taking precedence when duplicate keys exist.

Syntax

The basic syntax for merging arrays with original keys is −

$result = $array1 + $array2;

Example 1: Merging Arrays with Different Keys

Here's how to merge two associative arrays with unique keys −

<?php
    $arr1 = array("p"=>"150", "q"=>"100", "r"=>"120", "s"=>"110");
    $arr2 = array("t"=>"115", "u"=>"103", "v"=>"105", "w"=>"125");
    var_dump($arr1 + $arr2);
?>

array(8) {
    ["p"]=> string(3) "150"
    ["q"]=> string(3) "100"
    ["r"]=> string(3) "120"
    ["s"]=> string(3) "110"
    ["t"]=> string(3) "115"
    ["u"]=> string(3) "103"
    ["v"]=> string(3) "105"
    ["w"]=> string(3) "125"
}

Example 2: Merging with Empty Array

When one array is empty, the union operator simply returns the non-empty array −

<?php
    $arr1 = array();
    $arr2 = array("a" => "Jacob");
    var_dump($arr1 + $arr2);
?>

array(1) {
    ["a"]=>
    string(5) "Jacob"
}

Example 3: Handling Duplicate Keys

When arrays have duplicate keys, values from the left array take precedence −

<?php
    $arr1 = array("name" => "John", "age" => 25);
    $arr2 = array("name" => "Jane", "city" => "New York");
    var_dump($arr1 + $arr2);
?>

array(3) {
    ["name"]=>
    string(4) "John"
    ["age"]=>
    int(25)
    ["city"]=>
    string(8) "New York"
}

Key Points

• The + operator preserves original keys from both arrays
• Values from the left array override duplicate keys
• Order matters: $arr1 + $arr2 differs from $arr2 + $arr1
• Unlike array_merge(), the union operator maintains key associations

Conclusion

The array union operator (+) is the simplest method to merge arrays while preserving original keys. It's particularly useful when you need to combine configuration arrays or maintain key-value relationships during array operations.