foreach(@aoh)
{
   my %a = %$_;
   my %c= reverse %a;
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The problem with reversing the hash is that if the values aren't unique, e.g.

 {
    3 => 15,
    4 => 8,
    5 => 8,
 },
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you won't get the desired result...  So why impose unnecessary restrictions for no real gain?  For any reasonably sized hash, creating a reversed copy of it will approximately outweigh the benefits of not having to dereference in the sort function.

Also, there's no need to create an extra temp hash %a, just write

   my %c = reverse %$_;
[download]