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<?php $a = [ 'a' => 0, 'b' => 0, 'c' => 1 ]; var_export( array_reduce( array_keys($a), function ($result, $k) use ($a) { $result[$a[$k]][] = $k; return $result; } ) );
Output for 8.1.0 - 8.1.28, 8.2.0 - 8.2.19, 8.3.0 - 8.3.7
array ( 0 => array ( 0 => 'a', 1 => 'b', ), 1 => array ( 0 => 'c', ), )
preferences:
79.85 ms | 402 KiB | 62 Q