Maybe you should write to a new hash if you can't be sure about the risk of losing information overwriting 2D symmetries. (Imagine keys A and B being from the same set of values, like indices of a matrix)

Afaik should delete return the deleted value, such that you can do it in a one-liner

Otoh no need to delete when writing a new hash.

Cheers Rolf
(addicted to the Perl Programming Language and ☆☆☆☆ :)
Je suis Charlie!

In reply to Re^2: inverting keys in a 2-D Hash by LanX
in thread inverting keys in a 2-D Hash by melmoth

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