Isn't this pretty much what I had in the first place?

Having re-inspected your code, yes. Kinda. I didn't recognise as such the first time I looked.

That does raise a question though. Why do you think it is inefficient?

The cost of building @choices (your @rndselect) is a one-off up front cost. And hardly onorous at that unless you have thousand or millions of choices.

The actual runtime cost: $choices[ rand @choices ]; is as minimal as it is possible to be, and totally fair. One random number generation and one access to the array.

The only real alternative to it (for fairness) is the Knuth algorithm and from memory that requires you to:

  1. Pick a random number;
  2. traverse (on average) half the weights array (or hash) accumulating the weights until the sum is greater than the random number you picked.
  3. Then obtain the number (either from a parallel array or the hash).

So O(N(/2)) compared to O(1).

If you have sufficient choices that the memory for the array is a concern, then pack indexes into a string and cut your memory requirement to 1/8th.

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.
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In reply to Re^3: Weighted random selection by BrowserUk
in thread Weighted random selection by cosmicperl

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