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randperm

Random permutation of integers

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Syntax

p = randperm(n)
p = randperm(n,k)
p = randperm(s,___)

Description

p = randperm(n) returns a row vector containing a random permutation of the integers from 1 to n without repeating elements.

example

p = randperm(n,k) returns a row vector containing k unique integers selected randomly from 1 to n.

example

p = randperm(s,___) generates a random permutation of integers from random number stream s instead of the default global stream. To create a stream, use RandStream. Specify s followed by any of the argument combinations in previous syntaxes.

Examples

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Open Live Script

Generate a random permutation of the integers from 1 to 6. The input to randperm indicates the largest integer in the sampling interval (the smallest integer in the interval is 1).

r = randperm(6)
r = 1×6

     6     3     5     1     2     4
Open Live Script

Generate a random permutation of four unique integers (without repeating elements) selected randomly from the integers 1 to 8.

r1 = randperm(8,4)
r1 = 1×4

     6     4     7     3

Generate another random permutation of four unique integers.

r2 = randperm(8,4)
r2 = 1×4

     8     7     5     4
Open Live Script

Save the current state of the random number generator and create a random permutation of the integers from 1 to 8.

s = rng;
r = randperm(8)
r = 1×8

     6     3     7     8     5     1     2     4

Restore the state of the random number generator to s, and then create a new random permutation of the integers from 1 to 8. The permutation is the same as before.

rng(s)
r1 = randperm(8)
r1 = 1×8

     6     3     7     8     5     1     2     4

You can use the rng function to specify the settings of the random number generator.

Input Arguments

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Number of integers in sample interval, specified as a positive integer. randperm permutes integer values from 1 to n inclusive.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64

Number of selected integers, specified as a positive integer. k must also be less than or equal to n.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64

Random number stream, specified as a RandStream object.

Example: s = RandStream('dsfmt19937'); randperm(s,10)

More About

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Pseudorandom Number Generator

The underlying number generator for randperm is a pseudorandom number generator, which creates a deterministic sequence of numbers that appear random. These numbers are predictable if the seed and the deterministic algorithm of the generator are known. While not truly random, the generated numbers pass various statistical tests of randomness, satisfying the independent and identically distributed (i.i.d.) condition, and justifying the name pseudorandom.

Tips

  • The sequence of numbers produced by randperm is determined by the internal settings of the uniform pseudorandom number generator that underlies rand, randi, randn, and randperm. To control that shared random number generator, use the rng function.

  • The arrays returned by randperm contain permutation of integers without repeating integer values. This behavior is sometimes referred to as sampling without replacement. If you require repeating values, use the randi function.

  • randperm(n) and randperm(n,n) both generate permutations of the integers 1 through n, but they can give different random orderings in the permutations. For large n, randperm(n,n) is faster than randperm(n).

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

Version History

Introduced before R2006a

See Also

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