Randomly choose any number of elements within a given sample randomly

Question

If I want to arbitraraly choose any number $(1\sim9)$ of arbitrarily elements within $(1\sim9)$:

Ex:
1. $n = 3$ (randomly) $\rightarrow$ choose $"1,4,9"$ (randomly & no repeat)
2. $n = 2$ (randomly) $\rightarrow$ choose $"9,10"$ (randomly & no repeat)

How to use Matlab to implement it?

I know randsample; however, randsample can only choose one value randomly.
Use for loop. The bad news is this method will repeat the choice.

Any good way?

randsample can choose more than one element, without replacement (otherwise it would be the same as randi); see my answer — Luis Mendo, Jun 23 '15 at 21:46

Empy2 · Answer 1 · 2015-06-24T12:04:29.983

1

[a,b]=sort(rand(1,9));b([1 2 3])
EDIT
There are a lot more sets of five-from-nine than one-from-nine. If you want to make all these sets equally likely, (and so choose five of them more often than one of them), you could do

result = find(rand(1,9)>0.5);

This has the disadvantage that, once in 512, you get no numbers :(

edited Jun 24 '15 at 12:04

answered Jun 23 '15 at 09:19

Empy2

50,853

not quite exactly, it seems it cannot arbitrarily choose any number of elements because of b([1 2 3]), in which you have to choose three elements. How to do this step automatically? – sleeve chen Jun 23 '15 at 10:05
Here is one way: n = randam(9,1), b([1:n]). This correction might be helpful to this problem, thank you – sleeve chen Jun 23 '15 at 10:09
1

One correction: n=randsample(9,1) – sleeve chen Jun 23 '15 at 10:33
I must have an old version of Matlab – Empy2 Jun 23 '15 at 10:45

Luis Mendo · Accepted Answer · 2015-06-23T21:48:00.770

1

n = randi(9); % number of elements to pick: choose uniformly between 1 and 9
result = randsample(9, n); % pick n elements from 1,...,9 uniformly without replacement

edited Jun 23 '15 at 21:48

answered Jun 23 '15 at 21:42

Luis Mendo

1,834

Randomly choose any number of elements within a given sample randomly

2 Answers2