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<?php $array1 = Array ( "0" => Array ( "length" => 5, "width" => 3, "height" => 2 ) ); $array2 = Array ( "0" => Array ( "length" => 3, "width" => 3, "height" => 3 ), "1" => Array ( "length" => 5, "width" => 5, "height" => 5 ), "2" => Array ( "length" => 5, "width" => 5, "height" => 5 ) ); $array2[] = $array1[0]; print_r($array2);
Output for 5.6.0 - 5.6.26, 7.0.0 - 7.0.20, 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 - 8.1.28, 8.2.0 - 8.2.19, 8.3.0 - 8.3.7
Array ( [0] => Array ( [length] => 3 [width] => 3 [height] => 3 ) [1] => Array ( [length] => 5 [width] => 5 [height] => 5 ) [2] => Array ( [length] => 5 [width] => 5 [height] => 5 ) [3] => Array ( [length] => 5 [width] => 3 [height] => 2 ) )

preferences:
116.13 ms | 404 KiB | 188 Q