How to Merge Numerically-Keyed Arrays in PHP While Preserving Original Keys?

Merging Numerically-Keyed Associative Arrays While Preserving Original Keys

When merging two associative arrays with numerically-keyed indices, it's common to encounter issues preserving both the elements and their original keys. Consider the following arrays:

array(
    '11' => '11',
    '22' => '22',
    '33' => '33',
    '44' => '44'
);

array(
    '44' => '44',
    '55' => '55',
    '66' => '66',
    '77' => '77'
);

Using array_unique( array_merge( $array1 , $array2 ) ) may seem like a solution, but it alters the original keys.

Solution 1: Using array_merge and array_combine

Use array_merge to combine the arrays and array_combine to recreate the original keys:

$output = array_merge($array1, $array2);
$output = array_combine($output, $output);

Solution 2: Using the Array Merge Union Operator ( )

A convenient solution is to use the array merge union operator ( ):

$output = $array1 + $array2;

Result:

In both cases, the resulting array will preserve the original keys and contain all unique elements:

array(
    '11' => '11',
    '22' => '22',
    '33' => '33',
    '44' => '44',
    '55' => '55',
    '66' => '66',
    '77' => '77'
);

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