If you want several samples without replacement, shuffle is useful

If you want several samples with replacement, convert to a vector, then (vector-ref v (random (vector-length v))) can be good enough. If you require strong statistical guarantees, i think the math collection has some tools

And take

This is simpler but less efficient than doing proper reservoir sampling as sorawee suggests

Thanks :blush:

use random-ref, it works with any sequence

there’s also random-sample if you’re selecting multiple elements

Wow, didn’t know about random-ref before!

Just peeked at the source code. It’s doing reservoir sampling.

me neither, although it’s been there for a while (6.4)!

Very nice, Bogdan! Thanks for the demonstration! I appreciate that!

Ugh, I think I implemented reservoir sampling at least once without knowing it was there.

Ditto! Will a search for “reservoir” in the docs find random-ref ?

I think there’s a way to add some magic to the docs for random-sample / random-ref so it shows up when reservoir is searched