# same values using randi setting seed as default

14 views (last 30 days)
Salvatore Mazzarino on 21 Sep 2012
I'm using randi to generate rand integer valeus but I get the same values two times in my vector. example
rng default;
for i = 1:4
heads(i) = randi(10);
end
heads =
9
10
2
10
I wouldn't get the same values. I would get a vector where every values is different. I have to set rng default in this way I can obtain at every run of my scripts the same randi values.
##### 0 CommentsShowHide -1 older comments

Sign in to comment.

### Accepted Answer

Sean de Wolski on 21 Sep 2012
See randperm if you do not want duplicate values:
randperm(10,4)
##### 2 CommentsShowHide 1 older comment
Sean de Wolski on 21 Sep 2012
The second argument was added in 11b I believe when randperm was rewritten as builtin.

Sign in to comment.

### More Answers (4)

Wayne King on 21 Sep 2012
Edited: Wayne King on 21 Sep 2012
I'm not sure exactly what you're asking here. If you are calling
randi(10)
even a small number of times (here 4 times), then I would expect that you would get repeated values with a substantial probability. There are only ten values to choose from.
With respect to:
I wouldn't get the same values. I would get a vector where every values is different. I have to set rng default in this way I can obtain at every run of my scripts the same randi values.
If you use rng with a seed, then you will obtain the same values every time. Are you asking for a seed where you will get 4 different values?
For example:
rng(100)
x = randi(10,4,1);
Also, why are you going randi() in a for loop like that, you can just create a vector and be done with it.
To recreate your example:
rng default;
x = randi(10,4,1);
##### 2 CommentsShowHide 1 older comment
Wayne King on 21 Sep 2012
then if you want some randomness, don't seed and call randi(), use Sean's suggestion below.

Sign in to comment.

Peter Perkins on 21 Sep 2012
As others have said, randi is for "sampling with replacement", while randperm is for "sampling without replacement". If you happen to have the Statistics Toolbox, you will also find the datasample function (a newer replacement for randsample) that provides both kinds of sampling, as well as weighted versions of both.
You code snippet showed a loop with repeated calls to randi. If you need to be able to sample without replacement from 1:n in repeated calls, you'll need to maintain some kind of record of what values have already been drawn. That's not hard to do, but the magic of nested functions allows you to do this in a very nice way:
function s = makeWORSampler(n)
last = 0;
values = randperm(n);
s = @worSampler;
function x = worSampler(k)
if last+k > n
error('Not enough values remaining to be sampled.');
end
x = values(last+(1:k));
last = last + k;
end
end
>> s = makeWORSampler(10)
s =
@makeWORSampler/worSampler
>> s(5)
ans =
8 9 2 10 3
>> s(4)
ans =
7 4 1 5
>> s(1)
ans =
6
>> s(1)
Error using makeWORSampler/worSampler (line 7)
Not enough values remaining to be sampled.
Hope this helps.
##### 0 CommentsShowHide -1 older comments

Sign in to comment.

Daniel Shub on 21 Sep 2012
Do you want something like
temp = randperm(10);
heads = temp(1:4)
In this way heads will always have 4 values. These values will be chosen without replacement from the integers between 1 and 10 inclusive.
##### 0 CommentsShowHide -1 older comments

Sign in to comment.

Javier on 21 Sep 2012
Edited: Javier on 21 Sep 2012
Go to the help of Matlab (mine M2012Ra) and search for "Updating Your Random Number Generator Syntax"
for i = 1:4
rng('shuffle');
heads(i) = randi(10);
end
Consider also Mr King answer.
Javier
##### 0 CommentsShowHide -1 older comments

Sign in to comment.

### Categories

Find more on Random Number Generation in Help Center and File Exchange

### Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!