I have 2 arrays with different sizes, in some cases one array can have more elements than the other array. However, I always need to compare the arrays using the same id. I need to get the other value with the same id in the other array I have tried this, but the problem happens when I compare the two arrays in a loop when the other array has more elements than one, because duplicate the loop and data , and it does not work. Here is what I've tried: <?php /// Actual Data Arrays /// $data_1=array("a1-fruits","b1-apple","c1-banana","d1-chocolate","e1-pear"); $data_2=array("b1-cars","e1-eggs"); /// for ($i=0;$i<count($data_1);$i++) { /// Explode ID $data_1 /// $exp_id=explode("-",$data_1[$i]); /// for ($h=0;$h<count($data_2);$h++) { /// Explode ID $data_2 /// $exp_id2=explode("-",$data_2[$h]); /// if ($exp_id[0]=="".$exp_id2[0]."") { print "".$data_2[$h].""; print "<br>"; } else { print "".$data_1[$i].""; print "<br>"; } /// } /// } ?> I want the following values : "a1-fruits" "b1-cars" "c1-banana" "d1-chocolate" "e1-eggs" Yet, I get this (which isn't what I want): a1-fruits a1-fruits b1-cars b1-apple c1-banana c1-banana d1-chocolate d1-chocolate e1-pear e1-eggs I tried everything I know and try to understand how I can do this because I don't understand how to compare these two arrays. The other problem is when one size has more elements than the other, the comparison always gives an error. I FIND THE SOLUTION TO THIS AND WORKING IN ALL : <?php /// Actual Data Arrays /// $data_1=array("a1-fruits","b1-apple","c1-banana","d1-chocolate","e1-pear"); $data_2=array("b1-cars","e1-eggs","d1-chocolate2"); /// for ($i=0;$i<count($data_1);$i++) { $show="bad"; /// Explode ID $data_1 /// $exp_id=explode("-",$data_1[$i]); /// for ($h=0;$h<count($data_2);$h++) { /// Explode ID $data_2 /// $exp_id2=explode("-",$data_2[$h]); /// if ($exp_id2[0]=="".$exp_id[0]."") { $show="ok"; print "".$data_2[$h]."<br>"; } /// } if ($show=="bad") { print "".$data_1[$i].""; print "<br>"; } /// } ?>