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<?php $reference = [ 'a' => 'this is A', 'b' => 'here is B', 'c' => 'C here', 'd' => 'finally, d', ]; $indexesToKeep = [1, 3]; $lookup = array_flip($indexesToKeep); $index = 0; $result = []; foreach ($reference as $key => $value) { if (isset($lookup[$index])) { $result[$key] = $value; } ++$index; } var_export($result);

preferences:
22.06 ms | 475 KiB | 4 Q