Create Unique Randomsample 1000 times

Hi Everyone,

I want to create a matrix based on 1000 random samples of 50 numbers selected from 1 to 100, as follows:

a = [];
for i =1:n
    y = randsample(100,50);
    a = horzcat(a,sort(y));
end

Here the variable "a" should have 1000 fields for 50 random numbers selected from 1 to 100

I want to make sure that the numbers are unique for each field. Does anyone know the best way to do this?

Thanks

Answer 1

[Jan]

a = zeros(n, 50);
for i =1:n
  a(i, :) = sort(randsample(100,50));
end

[EDITED] Or do you mean that the rows should be guaranteed to be different? Then:

% Rejection method:
a = zeros(n, 50);
i = 0;
while i < n
  v = sort(randperm(100, 50));
  if ~any(all(a(1:i, :) == v, 2))
    i       = i + 1;
    a(i, :) = v;
  end
end

[Steve Sous]

Thank you for your reply!

I might have misinterpreted what I need. The code you wrote still invokes the randample function separately 1000 times. Does that guaranty that the 1000 random samples (50 each) from a(i=1:1000,:) are unique?

Thank you

[José-Luis]

Yes.

[Jan]

See [EDITED]

Answer 2

[Akira Agata]

Just in case, you can check the uniqueness by:

% Make a variable 'a'
a = zeros(1000, 50);
for i =1:1000
  a(i, :) = sort(randsample(100,50));
end

% Check the uniqueness
isUnique = true(1000,1); 
for i =1:1000
  if length(unique(a(i,:))) ~= 50
    isUnique(i) = false;
  end
 end
any(~isUnique)

[Steve Sous]

I think I might be missing something! The suggested code does not give nonunique values. For example, if I add the following code line in the middle:

a(10,:) = a(1,:);

Which forces a replicate, the any(~isUnique) is still 0

Here is the full code

% Make a variable 'a'
a = zeros(1000, 50);
for i =1:1000
  a(i, :) = sort(randsample(100,50));
end

%Added Line  
a(10,:) = a(1,:);

% Check the uniqueness
isUnique = true(1000,1); 
for i =1:1000
  if length(unique(a(i,:))) ~= 50
    isUnique(i) = false;
  end
 end
any(~isUnique)

[Akira Agata]

Well, I don't understand your point clearly.

In my previous code, each row of a contains unique 50 random number. That means length(unique(a(k,:))) is always 50 for all k (=1:1000). Therefore, even if you add the line "a(10,:) = a(1,:);", the output any(~isUnique) becomes 0 and there is no strange point in this behavior.

So, I would be happy if you could explain clearly what is the point and what kind of output you want to obtain.