How to Efficiently Prefix Array Keys in PHP?

Prefixing Array Keys Efficiently

To prepend a string to the beginning of all keys in an array, there are multiple approaches available.

One-Line Solution

The most concise solution involves a combination of array_map and array_combine:

<code class="php">$prefix = "prefix";
$array = array_combine(
    array_map(
        fn($k) => $prefix . $k,
        array_keys($array)
    ),
    $array
);</code>

Functional Approach

For versions of PHP 7.4 and above, an arrow function syntax can be employed:

<code class="php">$prefix = "prefix";
$array = array_combine(
    array_map(
        fn($k) => $prefix . $k, 
        array_keys($array)
    ),
    $array
);</code>

Iterative Approach

A traditional loop-based solution is also available:

<code class="php">foreach ($array as $k => $v) {
    $array[$prefix . $k] = $v;
    unset($array[$k]);
}</code>

Pre-PHP 5.3 Custom Class

For older PHP versions, a custom class with a mapArray method can be used:

<code class="php">class KeyPrefixer {
    public function prefix(array $array, $prefix) {
        return $this->mapArray($array);
    }

    public function mapArray(array $array) {
        return array_combine(
            array_map(array($this, 'mapKey', array_keys($array)),
            $array
        );
    }

    public function mapKey($key) {
        return $this->prefix . (string)$key;
    }
}

$prefix = "prefix";
$array = KeyPrefixer::prefix($array, $prefix);</code>

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