Thanks a lot for fix and comment.

I was careless for the order as you pointed out.

my @uniqIDs = grep{!$seen{$_}++}@IDs;
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with this, I can make use of the original order. And with List::MoreUtils, I can use unique or distinct keeping its order.

There seems to be a lot of interesting functions in List::MoreUtils. mesh,natatime and each_array ...umm... It is very interesting and I saw moritz often make use of them.

I have one perl 5.8 box and I would be burned if I didn't know that "each can return index for an array" is an functionality of 5.12.

regards