That is a good suggestion too -- I could run the code in blocks, saving up the deletions, and doing a clean-up after each 1M iterations, then restarting the while loop. I will see how much longer it takes to run after restricting myself to deleting only deleting the most recent iteration reference, and if it is a problem, move to your idea as a Plan B.

Thanks for your help. Learning ... :)

In reply to Re^2: Stepping through a hash while modifiying its content by Gorgarian
in thread Stepping through a hash while modifiying its content by Gorgarian

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