How to generate random indicies?

I would like to generate k different random indices from 1 to N. One solution is randperm(N,k), however I do not need to shuffle the indicies. Are there any other solution directly generating idicies in order?

Answer 1

[Image Analyst]

Yes, but if they're not "shuffled" then they're not random, are they? So you can get indices in ascending numerical order from 1 to N this way:

indices = 1 : N;

If you want what you said, but just sorted , then sort them:

pseudoRandomIndices = sort(randperm(N, k), 'ascend');

[Mr M.]

k is less than N, so for example randperm(10,3) gives back 9,2,5 but I want them in order: 2,5,9

[Star Strider]

You have to use the entire ‘pseudoRandomIndices’ assignment. It returns them in ascending order:

N = 10;
k = 3;
pseudoRandomIndices = sort(randperm(N, k), 'ascend')

returns:

pseudoRandomIndices =

       2     6     8

[Mr M.]

I can sort! This is not the question!

The algorithm is unnecessarily complicated (computational cost is unnecessarily big for large N)

[Image Analyst]

We're not sure which algorithm you're thinking of, sort or randperms, but feel free to rewrite either one with a less complicated version of them. We're not going to do that for you. Good luck.

Answer 2

[Matt J]

This avoids sorting,

        idx=false(1,N);
        vals=1:N;

        idx(randperm(N, k))=1;

        result=vals(idx);