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<?php $array = Array ( '0' => (object)[ 'id' => 17, 'res_id' => 10, 'cat_id' => 3 ], '1' => (object)[ 'id' => 18, 'res_id' => 10, 'cat_id' => 4 ], '2' => (object)[ 'id' => 52, 'res_id' => 19, 'cat_id' => 1 ], '3' => (object)[ 'id' => 53, 'res_id' => 19, 'cat_id' => 3 ], '4' => (object)[ 'id' => 54, 'res_id' => 19, 'cat_id' => 4 ] ); $result = array_map(function($x){ return $x->cat_id; }, $array); print_r($result);
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 - 8.1.28, 8.2.0 - 8.2.19, 8.3.0 - 8.3.7
Array ( [0] => 3 [1] => 4 [2] => 1 [3] => 3 [4] => 4 )

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