Maxtrix copy and manipulation

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Fischer Zheng 2015-9-17

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编辑： Matt J 2015-9-18

采纳的回答： Star Strider

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I have one matrix and one vector. I would like to shift the elements of row forward depending on the vector index.

M = [0 2 4 5;
     0 4 7 9;
     0 0 0 34];
v = [4 3 2];

Shift the elements of M forward, v(1) = 4 indicate start result with the 4th element of the row. Pad the end of row with zeros.

Result = [5 0 0 0;
          7 9 0 0;
          0 0 34 0]

How do I do this in the vectorized way?

Thanks, Fischer

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Star Strider 2015-9-17

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This uses a loop, but I can’t see how to do this without one:

M = [0 2 4 5; 0 4 7 9; 0 0 0 34]; 
v = [4 3 2];
c = size(M,2);
Result = zeros(size(M));
for k1 = 1:size(M,1)
    Result(k1,1:c-v(k1)+1) = M(k1,v(k1):c);
end

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Fischer Zheng 2015-9-17

You are right, too bad.

Star Strider 2015-9-17

Thank you.

If you’re doing this once for each large matrix, save the shifted matrix to a .mat file. Then you can simply load the shifted matrix when you need it, rather than recalculating it each time.

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Matt J 2015-9-17

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https://ww2.mathworks.cn/matlabcentral/answers/243619-maxtrix-copy-and-manipulation#answer_192761

编辑：Matt J 2015-9-18

在 MATLAB Online 中打开

    v=v(:);
    [m,n]=size(M);
    [I,J,S]=find(M);
    J=J-v(I)+1;
    idx=J>0;
    Result=sparse(I(idx),J(idx),S(idx),m,n);
     Result=full(Result); %optional