MATLAB: How to remove repetition in matrix without changing length

Question

Hi,

I'm trying to create an experiment with matlab and I am using 2 columns in a matrix with number I have randomized according to an index.

I cannot however have a repetition within one column and the two columns have to stay separated and keep the length of 36 elements.

so this is how I created my matrix:

for n = 1:6
   l((n-1)*6+1:n*6,1)=n
   l((n-1)*6+1:n*6,2)=[1:6]
end
vec_index=randperm(36)
vec_randomised=l(vec_index',:)

which gives me this:

5     3
   4     2
   4     1
   4     6
   5     5
   6     3
   1     5
   1     2
   1     6
   6     5
   3     2
   6     1
   5     4
   1     4
   2     3
   3     5
   5     2
   2     2
   6     2
   4     3
   2     6
   3     6
   5     1
   2     5
   6     4
   2     1
   6     6
   3     4
   3     3
   4     4
   5     6
   1     1
   2     4
   3     1
   1     3
   4     5

as you can see there are repetitions for example the 3×4 in the first column.

I made a for-loop to detect the repetition but this does not help me to remove them and keeping the same numbers/amount of numbers in the column.

I also tried shuffle but this gives me different numbers.

I hope I need this as I want to couple this array to words and sounds (which I'm also failing at)

Hopefully someone can help! thx

Answer 1

with the size of your matrix, a brute force approach of generating a new permutation until it matches your requirement seems feasible. On the few test I did, it only took a maximum of 1 second:

%a better way to generate the original matrix:
numwords = 6;
numsounds = 6; %doesn't have to be the same number as numwords
wordperm = repmat(1:numwords, numsounds, 1);
wordsound = [wordperm(:), repmat([1:numsounds]', numwords, 1)];
%brute force search of random permutation with no two consecutive number in any column
tic
while any(any(diff(wordsound) == 0))
    wordsound = wordsound(randperm(numwords * numsounds), :);
end
toc
wordsound