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<?php $array = array( array("x1" => 1, "x2" => 3, "y5" => 9), array("x1" => 3, "x4" => 1, "y5" => 1), array("x1" => 1, "x8" => 5, "a5" => 2), array("x1" => 2, "x10" => 3, "b5" => 5) ); $keys = []; foreach($array as $subarr){ $keys = array_merge($keys, array_keys($subarr)); } foreach(array_unique($keys) as $item){ $res[$item] = array_sum(array_column($array, $item)); } var_dump($res);
Output for 7.1.0 - 7.1.20, 7.2.0 - 7.2.33, 7.3.16 - 7.3.33, 7.4.0 - 7.4.33, 8.0.0 - 8.0.30, 8.1.0 - 8.1.33, 8.2.0 - 8.2.29, 8.3.0 - 8.3.27, 8.4.1 - 8.4.14
array(8) { ["x1"]=> int(7) ["x2"]=> int(3) ["y5"]=> int(10) ["x4"]=> int(1) ["x8"]=> int(5) ["a5"]=> int(2) ["x10"]=> int(3) ["b5"]=> int(5) }

preferences:
157.16 ms | 408 KiB | 5 Q