Update: modified the code and benchmark results, which were actually meaningless, thanks to ikegami's wise and knowledgeable advice. And as he rightly predicted, the difference between each method really isn't that huge.
Also note that my solution does something slightly different than the others. In fact I tried to adhere strictly to the specifications as of the wanted input and output examples given in the first post. Indeed you'll notice that the 'c' key appears both lowercase and uppercase: this seems probable to be just a typo, which is why others plainly ignored it; but since you could deal with it just fine with virtually no more effort, I just did it -- for instructive reasons.

In reply to Re^2: Common elements of a hash of hashes by blazar
in thread Common elements of a hash of hashes by Anonymous Monk

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