Re: Random hash element (low memory edition).

You can find the number of elements using keys in a scalar context, and it won't take time or space to go through the elements.

But you could use the recipe for printing a random line from a file to just iterate through the hash without knowing how many elements it has and select a random one.

Yes, as long as you don't change the hash, keys will return keys in the same order every time. values will return values in the corresponding order.

Caution: Contents may have been coded under pressure.

Comment on Re: Random hash element (low memory edition). Select or Download Code

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Re^2: Random hash element (low memory edition). by amarquis (Curate) on Jan 24, 2008 at 20:51 UTC
That method is awfully neat, but my perl skills are not so I'll hit you with a follow-up question. `rand($.) < 1 && ($line = $_) while <>;` So this iterates through the file and, if a random number from 0 to the current line number is less than 1, selects the current line, overwriting previous choices? So, in my case, I'd just keep a count variable for how many elements I've been through and use that in place of $.? I'm going to have to check out the proof of that, it is really interesting that everything evens out (i.e. the first elements have a high chance of being overwritten, the latter elements have a high chance of just not being picked, and it all balances out to a random selection.) Thanks for pointing me to that FAQ entry!	[reply] [d/l]
Re^3: Random hash element (low memory edition). by Roy Johnson (Monsignor) on Jan 24, 2008 at 21:06 UTC
So, in my case, I'd just keep a count variable for how many elements I've been through and use that in place of $.? Exactly. Caution: Contents may have been coded under pressure.	[reply]


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