vectorization - problem with zeros

Question

Julius 2012-6-23

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/41879-vectorization-problem-with-zeros

I need to expand a small matrix A into a bigger one according to a pattern defined by a an array R. But the array may contain zeros so as to know that the rows and columns marked''0'' should be omitted. Here are the matrices:

   A=[1 3 2 4;  R=[1;
      5 6 7 8;     3;
      9 1 2 3;     0;
      4 5 6 2];    7];
   R'=[1 3 0 7];
  % ... the resulting matrix would be:
  B=[1 0 3 0 0 0 4;
     0 0 0 0 0 0 0;
     5 0 6 0 0 0 8;
     0 0 0 0 0 0 0;
     0 0 0 0 0 0 0;
     0 0 0 0 0 0 0;
     4 0 5 0 0 0 2];

B=zeros(7,7); B(R,R')=A ......returns an error

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Luffy 2012-6-23

I do not think you can write B(R,R') as Subscript indices must either be real positive integers or logicals.

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Answer 1

Julius 2012-6-23

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https://ww2.mathworks.cn/matlabcentral/answers/41879-vectorization-problem-with-zeros#answer_51562

在 MATLAB Online 中打开

Thank you Monkey, I really appreciate your help, but it seems that I've found a more effective solution:*

A=[1 3 2 4;  
   5 6 7 8;     
   9 1 2 3;     
   4 5 6 2]; 
R=[1 3 0 7];
B=zeros(7);
    RNZ=R(R ~= 0);   
    d=find(R);
    T=A(d,d');
    B(RNZ,RNZ')=T

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Answer 2

Luffy 2012-6-23

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https://ww2.mathworks.cn/matlabcentral/answers/41879-vectorization-problem-with-zeros#answer_51561

在 MATLAB Online 中打开

 A(find(R==0),:)=0;  % on doing this u make a row of A=0 at which R=0 assuming there is only 1 zero in R  as per you example otherwise add a for loop.
A =  [1     3     2     4;
      5     6     7     8;
      0     0     0     0;
      4     5     6     2];
 A(:,find(R'==0))=0;  % on doing this u make a column of A=0 at which R'=0 assuming there is only 1 zero in R  
A =  [1     3     0     4;
      5     6     0     8;
      0     0     0     0;
      4     5     0     2];
 B = zeros(7); % to create bigger matrix B,i took it as per your example as 7X7 matrix, 
B =   [ 0     0     0     0     0     0     0;
        0     0     0     0     0     0     0;
        0     0     0     0     0     0     0;
        0     0     0     0     0     0     0;
        0     0     0     0     0     0     0;
        0     0     0     0     0     0     0;
        0     0     0     0     0     0     0];
j = 1;
 for i =1:2:length(B(1,:))
 l = 1;
 for k = 1:2:length(B(:,1))
 B(i,k) = A(j,l);
 l = l+1;
 end
j = j+1;
end
B;
 B =    [    1     0     3     0     0     0     4;
             0     0     0     0     0     0     0;
             5     0     6     0     0     0     8;
             0     0     0     0     0     0     0;
             0     0     0     0     0     0     0;
             0     0     0     0     0     0     0;
             4     0     5     0     0     0     2];
% this should  give you answer you are looking for
% I am not generally good at following coding practices,if u do not understand any part feel free to comment