randomly select different elements of a vector

Hello,

I am looking to select n random elements from a vector, but none of the elements can be the same. for example x=[1 1 1 2 3 4 4 4 5 6 7 7], I want to select 4 random unique elements from x, giving 1, 4, 7, 6.

Thanks

Steve

Answer 1

[Thorsten]

x = [1 1 1 2 3 4 4 4 5 6 7 7];
 for i = 1:4
   ind = randperm(numel(x), 1); % select one element out of numel(x) elements, with the probability of occurrence of the element in x
   r(i) = x(ind);
   x(x==r(i)) = []; % delete this element from the sample, such that the picked elements are unique
 end

[stephen cusack]

Thanks!!

Answer 2

[the cyclist]

x=[1 1 1 2 3 4 4 4 5 6 7 7];
ux = unique(x);
rx = randsample(ux,4,false);

Note that this will break if there are fewer than four unique elements in x, but it is easy to put in a safeguard against that. For example,

rx = randsample(ux,min(numel(ux),4),false);

[stephen cusack]

Apologies I did not frame the question very well. I am looking to take the sample based on the occurrence of each element. So 1 has probability 3/12, 2=1/12, 3=1/12, 4=3/12, 5=1/12, 6=1/12, 7=2/12. Once one element has been chosen it cannot be selected again.

Answer 3

[Andrei Bobrov]

x=[1 1 1 2 3 4 4 4 5 6 7 7];

a = unique(x);
out = a(randperm(numel(a),4))

[stephen cusack]

Apologies I did not frame the question very well. I am looking to take the sample based on the occurrence of each element. So 1 has probability 3/12, 2=1/12, 3=1/12, 4=3/12, 5=1/12, 6=1/12, 7=2/12. Once one element has been chosen it cannot be selected again.