`randperm`

Random permutation of the integers 1 to n.

Category: Mathematics > Random Number Generation

Syntax

p = randperm(n)

Returns a row vector with the integers 1 to n in random order.

p = randperm(n, k)

Returns k unique integers chosen at random from 1:n.

p = randperm(s, ___)

Uses the RandStream object s instead of the global stream.

Description

Every value appears at most once, so randperm samples without replacement. It is the usual way to shuffle: x(randperm(numel(x))) reorders a vector, and randperm(n, k) picks k random indices.

Input arguments

n: Nonnegative integer scalar.
k: Number of values to return, with 0 <= k <= n; otherwise it is an error.

Output arguments

p: Row vector of unique integers, every ordering equally likely.

Example

Shuffling and sampling

rng(1);
randperm(6)
randperm(10, 3)
x = [10 20 30 40];
x(randperm(4))

Output

ans = 1×6

     3     6     5     4     1     2
ans = 1×3

     2     4     9
ans = 1×4

    40    20    10    30

Notes

The order produced for a given seed may differ from the one MATLAB gives.

randperm