set zero in matrix elements

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Souvik Agasti
Souvik Agasti 2017-7-31
评论： the cyclist 2017-8-14
Hi, I have a 3d tensor in MATLAB. Call it A. Lets say, size(A)=[4 6 10]. I have another matrix M which holds few indexes of the first two dimensions of the matrix A. Like
M=[1 5;3 2;1 4];
Now, I want to set all elements of the matrix A as zero which has the different index (of the first two dimensions) than the matrix M. Basically, what I want to do is-
A((if index(A{1,2})~=M),:)=0
Please help me.

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the cyclist
the cyclist 2017-7-31
This is a little clunky, but it works.
A = rand(4,6,10);
M = [1 5;
3 2;
1 4;];
[a1,a2,a3] = size(A);
[m1,m2] = size(M);
subIndices = [repmat(M,a3,1),repmat((1:a3)',m1,1)];
linearIndicesToKeep = sub2ind([a1,a2,a3],subIndices(:,1),subIndices(:,2),subIndices(:,3));
linearIndicesToZero = setxor(linearIndicesToKeep,1:(a1*a2*a3));
A(linearIndicesToZero) = 0;
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Jan
Jan 2017-8-14
@Cyclist: What a pitty that there is no direct solution like:
B(M(:,1), M(:,2), :) = A(M(:,1), M(:,2), :)
This copies the rectangular sub-matrices but not the desired pages.
Instead of the XORing, I'd copy the wanted elements only:
B = zeros(size(A));
B(linearIndicesToKeep) = A(linearIndicesToKeep);
the cyclist
the cyclist 2017-8-14
@Jan: That direct solution is so logical that I tried it first.

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