Online PHP editor | refs for UcEYg

<?php $input = Array ( 'arr1' => Array ( 'JAN2016', 'MAI2013', 'JUN2014', ), 'arr2' => Array ( 'APR2016', 'DEC2013', 'JUN2014', ), 'arr3' => Array ( 'JAN2016', 'MAI2020', 'JUN2022', ) ); $newArray = []; foreach($input as $k=>$values) { foreach($values as $value) { $newArray[$value][] = $k; } } print_r(array_filter($newArray, function($v) { return 1 < count($v); }));