set zero in matrix elements

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.

Answer 1

[the cyclist]

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;

[Souvik Agasti]

Hi 'the cyclist',

Thanks a lot. But, I would like to make some change over it.

A = rand(4,6,10);

M = [1 5; 3 2; 1 4;];

[a1,a2,a3] = size(A);

[m1,m2] = size(M);

dimen3 = repmat((1:a3),m1,1);

subIndices = [repmat(M,a3,1), dimen3(:)];

linearIndicesToKeep = sub2ind([a1,a2,a3],subIndices(:,1),subIndices(:,2),subIndices(:,3));

linearIndicesToZero = setxor(linearIndicesToKeep,1:(a1*a2*a3));

A(linearIndicesToZero) = 0;

[Jan]

@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]

@Jan: That direct solution is so logical that I tried it first.