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PHP's functional array helpers:

$nums = [1, 2, 3, 4, 5];

$doubled = array_map(fn($n) => $n * 2, $nums);
// [2, 4, 6, 8, 10]

$evens = array_filter($nums, fn($n) => $n % 2 === 0);
// [2, 4]   — but keys are preserved! [1 => 2, 3 => 4]

$sum = array_reduce($nums, fn($acc, $n) => $acc + $n, 0);
// 15

A gotcha: array_filter preserves keys. To get a fresh 0-indexed array, wrap with array_values():

$evens = array_values(array_filter($nums, fn($n) => $n % 2 === 0));
// [2, 4]   — re-indexed [0 => 2, 1 => 4]

For more, see array_walk (mutate in place), array_combine (zip keys with values), array_flip (swap keys and values), array_unique (dedupe).