How Can I Preserve Original Keys When Merging Numerically-Keyed PHP Arrays?

Preserve Original Keys While Merging Numerically-Keyed Associative Arrays

When merging associative arrays with numerically-keyed elements, it's often desirable to retain the original key values. However, the array_merge function may overwrite or renumber keys when dealing with duplicate keys.

For instance, given arrays like these:

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

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

Attempting to merge these arrays using array_merge can lead to key changes:

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

This approach changes the output keys to 0-based integers.

To preserve the original keys, use the following method:

$output = $array1 + $array2;

By using the addition operator ( ), PHP merges the arrays and retains the original numerical keys. The result will be:

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

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