$arr = array( 0=>array('key1'=>'value1' , 'key2'=>'value2'), 1=>array('key1'=>'value1' , 'key2'=>'value3'), 2=>array('key1'=>'value2' , 'key2'=>'value4'), 999=>array('key1'=>'value2' , 'key2'=>'value5') ); $result = array(); foreach ($arr as $data) { isset($result[$data['key1']]) || $result[$data...