How to select k out of n, k being normally distributed but not exceeding n

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Daniel
Daniel 2014-5-13
评论： Matt J 2014-5-13
Hello everyone,
I need to select k numbers out of n without generating doubles and k must not exceed n.
I used to do it by first getting k with normrnd and a very low variation and then finding random numbers and checking for doubles until I have my set of k. Not a very nice approach I know.
Just now I found randperm and it allows me to do this more elegantly, but the prime use of that function, the permutation, is wasted effort in my use. I also switched from normrnd(mu,sigma) to mu+sigma*randn.
Does anyone know a more fficient way of doing this?
Thank you.

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回答（1 个）

Matt J
Matt J 2014-5-13
编辑：Matt J 2014-5-13
There is nchoosek(n,k).
It's not clear, however, what "k being normally distributed" is supposed to mean. Clearly, k is always a positive integer, so it cannot be normally distributed.
  2 个评论
Daniel
Daniel 2014-5-13
编辑：Daniel 2014-5-13
Thank you for the first part.
k should be normally distributed integer over the range 1 to n-1. Initially I ran into problems when k exceeded n and I solved it by decreasing the standard deviation. I am not happy with this, as it still leaves the problem unsolved. Do you have an idea how to do this better?
Edit: nchoosek is sadly not what I need. I don't need the binomial coefficient. I need one set of k numbers froom 0 to n.
Matt J
Matt J 2014-5-13
I still have no idea what a "normally distributed integer" means. It is definitely not standard terminology. Perhaps you mean a uniformly distributed integer, in which case you could use RANDI.

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