MATLAB: Expand vectors of matrix, but a different number of times each vector

expandmatrixstructuresvector

Hi all,

I have the following problem. Consider a matrix of the form

Z =[1 0 0 0; 1 0 0 0; 1 0 0 0; 0 0 0 1; 0 0 0 1];

Because I'll use this later, consider the vector that sums the elements of the matrix by rows:

C=[3 0 0 2];

I would like to take every column in Z and expand it according to the elements in C, when the expansion when C=0 is just the column itself, to get

D=[1 1 1 0 0 0 0; 1 1 1 0 0 0 0;1 1 1 0 0 0 0;0 0 0 0 0 1 1;0 0 0 0 0 1 1];

Some things to consider. I have a lot of matrices "Z". In particular, they are defined in a structure way. This means that, for example, I have mk(i).Z where i goes from 1 to, say, 50. This means that I also have 50 vectors "C" (mk(i).C). Finally, the Z's have different dimensions that I don't know ex-ante (they are generated randomly within the code).

Any help would be great, thanks

Fernando

Best Answer

z2 = cell2mat(cellfun(@(z,c)repmat(z,1,max(c,1)),num2cell(Z,1),num2cell(C),'uni',false))

Not sure why you need to do this though. It's going to take more memory to not get you any more information. If you could explain a little more, we might be able to help with a better way.

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MATLAB: Create new matrix with compine values

First, don't store your matrices in individual variables, it complicates everything. Since they're all the same size store them as pages of a 3D matrix:

M = cat(3, [0 0 1; 1 0 0; 1 0 1], [1 0 1; 1 1 1;1 1 1], [0 0 0 ; 1 0 0 ; 0 1 1],  [ 1 0 1;1 1 1; 1 0 0])

With that it's trivial to choose a combination of any 3 of the matrices:

selectedindices = randi(size(M, 4), 1, 3);  %select 3 indices at random

So, to get the result you want:

mean_ones = NaN;  %initial condition will always result in false, so we go at least once through the loop
while mean_ones < 3 | mean_ones < 6   %while we don't have a set that matches the criteria
    selectedindices = randi(size(M, 4), 1, 3);  %select 3 indices at random
    selectematrices = M(:, :, selectedindices);
    mean_ones = nnz(selectedmatrices) / 3;
end

edit: and if you want to generate all possible combinations or 3 matrices that follow your criteria, like fred did in his answer:

%M: 3D matrix as above
allcombs = dec2bin(0:size(M, 3)^3-1, size(M, 3)) - '0' + 1; %works for up to 10 matrices
allmatcombs = reshape(M(:, :, allcombs'), size(M, 1), size(M, 2), size(M, 3), []);
meanmat = sum(allmatcombs, 1:3) / 3; %requires 2018b or later. Earlier versions: sum(sum(sum(allmatcombs, 1), 2, 3) / 3
selectedmatcombs = allmatcombs(:, :, :, meanmat >= 3 & meanmat <= 6);

MATLAB: How to find the duration of a number in an array

c = c(:);
ii = [true;diff(c)~=0];
i2 = diff([find(ii);numel(ii)+1]);
[a,b,c0] = unique(c(ii),'first'); % in new version of MATLAB:
[~,jj] = sort(b);                 %


[~,j1] = sort(jj);                % [a1,~,c1] = unique(c(ii),'stable');         
a1 = a(jj);                       %
c1 = j1(c0);                      %
out = [a1,accumarray(c1,i2,[],@mean)];

or with sorting

ii = [true;diff(c)~=0];
i2 = diff([find(ii);numel(ii)+1]);
[a,~,c0] = unique(c(ii));
out1 = [a,accumarray(c0,i2,[],@mean)]

Best Answer

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MATLAB: Create new matrix with compine values

MATLAB: How to find the duration of a number in an array

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