How Can I Merge Numerically-Keyed Associative Arrays in PHP While Preserving Original Keys?

Merging Associative Arrays with Preserved Numerical Keys

When combining two numerically-keyed associative arrays, it's often desired to maintain the original keys in the combined array while avoiding duplicates. Here's a simple solution:

$array1 = [
    '11' => '11',
    '22' => '22',
    '33' => '33',
    '44' => '44',
];

$array2 = [
    '44' => '44',
    '55' => '55',
    '66' => '66',
    '77' => '77',
];

$output = $array1 + $array2;

In PHP, the operator for arrays merges two arrays, and when two keys with the same numerical value are present, the value from the right-hand array overwrites the value from the left-hand array. However, since the keys in this case are integers, PHP treats them as numbers and renumbers the keys.

To recreate the original numerical keys, use array_combine:

$output = array_combine($output, $output);

This creates a new array with the original keys restored.

Hence, the merged array with preserved numerical keys looks like this:

[
    '11' => '11',
    '22' => '22',
    '33' => '33',
    '44' => '44',
    '55' => '55',
    '66' => '66',
    '77' => '77',
]

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