create a randomised vector from matrix
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I'm relatively new to Matlab so this might be a very simple problem to solve: I have a 37 x 8 matrix (ascending order numbers, 1:296) I need to create a 296 x 1 vector in which each row will take a number from the matrix rows, with the exception that it cannot be the same row as the previous 8 rows.
Any help would be much appreciated!
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Answers (2)
Image Analyst
on 30 Jul 2016
Try this:
newVector = yourMatrix(:);
This will produce a column vector. No element of newVector will have come from the same row as any of the previous 8 elements of newVector did.
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Image Analyst
on 30 Jul 2016
I don't think it's possible to be totally random. You can use randperm(numel(yourMatrix)) to get a list of linear indexes in a random order, and then just keep trying until you get the condition where no element is in the same row as any other element within 8 elements of it, but I don't think you'll ever succeed. I believe you'll have to impose some kind of order onto it, which is what I did. Good luck trying tough. Let us know if you succeed, and post an actual example where it worked.
If your matrix were square you could arrange it in a Latin Square pattern https://en.wikipedia.org/wiki/Latin_square but I don't think there's any Latin rectangle pattern.
Azzi Abdelmalek
on 30 Jul 2016
A=reshape(1:37*8,37,8) % Example
[n,m]=size(A)
idx=cell2mat(arrayfun(@(x) randperm(n)', 1:m,'un',0)')
idy=zeros(size(idx));
for k=1:n
ii=find(ismember(idx,k));
idy(ii)=randperm(m)';
end
ixy=sub2ind([n m],idx,idy);
out=A(ixy)
2 Comments
Image Analyst
on 31 Jul 2016
I don't think this works. I added this check after the code:
% Let's see if any of the linear indexes is in the same row as any of the prior 8 indices
for k = 9:length(ixy)
% Get row of kth index
[rowk, colk] = find(A == ixy(k));
% Check prior 8 elements
for k2 = k-8 : k-1
% Get row of k2'th index.
% Find out the row in A where this number appears.
[rowk2, colk2] = find(A == ixy(k2));
% See if this row matches the row where ixy(k) lies.
if rowk2 == rowk
fprintf('Index %d and %d are both in row %d.\n', ixy(k), ixy(k2), rowk);
end
end
end
and it found lots of cases where an index was in the same row of the original A matrix as one of the prior 8 indexes.
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