How convert matrix to original form

Question

fatema saba 2015-12-22

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https://ww2.mathworks.cn/matlabcentral/answers/261408-how-convert-matrix-to-original-form

回答： Walter Roberson 2015-12-22

Hello I have a matrix with 100 rows and 100 columns named it D. in fact this matrix was a matrix with 137 rows and 127 columns but some rows and columns remove because every elements of them was zero. ok, matrix D is like and indexing matrix. let to explain it. the first row and first column of this matrix show the true number of row and column of elements whitin the matrix. I want to expand this matrix and change it to original form with aid of the first row and the first column. Is it possible to guide me? below is part of matrix D as example:

    DD=[0 3 5 10 21 26 30;2 0 0 0.5 1 0 0;10 0 1 1 1 1 0;21 1 1 1 1 0.75 0;22 1 1 1 1 1 0.5;23 1 1 1 1 1 1;30 1 1 1 1 1 1;34 1 1 1 1 1 1;45 0 0 0 1 1 1;46 0 0 0 0 0 0;47 1 0.75 1 0.58 0.33 0.16;70 0.39 0.58 0.79 1 0 1;71 0 0 0.19 0 0 0;72 0 0 0.29 1 1 1;73 0.5 0 0 0 0 0]

Thank you.

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Answer 1

jgg 2015-12-22

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在 MATLAB Online 中打开

This loops, but it should be fast enough for your purposes, and it's easy to read, so you can probably figure out how to vectorize it easily enough.

 r = max(DD(:,1));
 c = max(DD(1,:));
 rowinds = DD(:,1);
 colinds = DD(1,:);
 original = zeros(r,c);
 for i = 2:size(DD,1)
   for j = 2:size(DD,2)
       original(rowinds(i),colinds(j)) = DD(i,j);
   end
 end

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Answer 2

Walter Roberson 2015-12-22

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https://ww2.mathworks.cn/matlabcentral/answers/261408-how-convert-matrix-to-original-form#answer_204081

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 rowinds = DD(2:end,1);
 colinds = DD(1,2:end);
 r = max(rowinds);
 c = max(colinds);
 original = zeros(r,c);
 original(rowinds,colinds) = DD(2:end,2:end);