Deleting elements from an array while iterating over it is explicitly documented as 'So don't do that' in perlfunc.
Yes, this is really getting bad and messy. But for some reason, it seems that it sort of works fine with a hash. I had a program where I was progressively "improving" my hash by deleting useless elements, and everything went fine. Then I thought that it might be more efficient to use an array instead, and I figured out that it did not work at all. The array got completely messed up. In brief, it seems that you can delete records from a hash while processing it, but can"t do it in an array. OK, maybe I got it wrong and did not understand fully what was going on, but I got the feeling that you can modify a hash while processing it with the keys function, but not an array fith the foreach function.
Does any monk here have an explanation for this apparently different behavor?