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RANDSUBSET

23 Jun 2010 (Updated 29 Jun 2010)

Return a random subset of k elements of the set of n elements

File Information

Description

A = RANDSUBSET(N, K) is equivalent to

ALLSUBSETS = NCHOOSEK(1:N,K);
A = ALLSUBSETS(RANDI(NCHOOSEK(N,K)));

% or

A = RANDPERM(N);
A = SORT(A(1:k));

This function can also be used to generate random sampling without replacement by calling RANDPERM on the output.

It works advantageously with large N (but "reasonable" K), and fast!

MATLAB release

MATLAB 7.10 (2010a)

Other requirements

Mex correctly setup

Tags for This File
Everyone's Tags	permutation, random, randperm, subset, without replacement
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Comments and Ratings (1)
25 Jun 2010	Bruno Luong	For the moment, it is not recommended using this function for k larger than 1e4, since the insertion complexity is O(k^2), which is not optimal. I'll work for the better insertion algorithm for the next release.

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Updates
24 Jun 2010	Mex engine
29 Jun 2010	Change the description