# choose elements from array randomly

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Majid Al-Sirafi on 23 Sep 2012
Hi everyone
I have vector array of elements …
for example a=[1,2,3,4]
how can I choose randomly 10% of the above array????
majid

Wayne King on 23 Sep 2012
You must be using an older version of MATLAB, do this instead:
% create vector
a = randn(100,1);
% determine how many elements is ten percent
numelements = round(0.1*length(a));
% get the randomly-selected indices
indices = randperm(length(a));
indices = indices(1:numelements);
% choose the subset of a you want
b = a(indices);

#### 1 Comment

Majid Al-Sirafi on 23 Sep 2012
thank you brother
majid

Wayne King on 23 Sep 2012
Edited: Wayne King on 23 Sep 2012
One thing you can do is:
% create vector
a = randn(100,1);
% determine how many elements is ten percent
numelements = round(0.1*length(a));
% get the randomly-selected indices
indices = randperm(length(a),numelements);
% choose the subset of a you want
b = a(indices);

Majid Al-Sirafi on 23 Sep 2012
thank you dear
but when I run this code the following error had been occured
??? Error using ==> randperm Too many input arguments.
majid
Wayne King on 23 Sep 2012
See my answer below for a use of randperm compatible with earlier versions of MATLAB

Azzi Abdelmalek on 23 Sep 2012
Edited: Azzi Abdelmalek on 23 Sep 2012
a=[1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17]
n=length(a)
nr=round(n/10)
out=a(randperm(n,nr))
or if you have'nt randperm
n=length(a);
nr=round(n/10)
[ ~,idx]=sort(rand(n,1));
out=a(idx(1:nr))

#### 1 Comment

Azzi Abdelmalek on 23 Sep 2012
Depends on how you want to round your percentage use, round or ceil or floor