2d matrix of index to get value of 3D matrix

Hello,

I have matrix A with size (37,30,1000); and a matrix B with size (37,1000). I want to use matrix B as a matrix of indexes to get value from A.

The index refers to which column in 3D matrix I want to get the value for each 1st and 3rd dimension.

Is there anyone having an idea how to solve it (prefer not using loop).

Thank you,

[jonas]

"The index is to index which column(2nd dimension) in 3D matrix for each 1st and 3rd dimenssion."

My head almost exploded reading this sentence. Care to elaborate?

[heidi pham]

sorry for my bad expression. I just edited it, hope it clearer now :)

[Stephen23]

Original question:

https://www.mathworks.com/matlabcentral/answers/425750-sub2ind-get-values-of-3d-matrix-using-an-index-vector

Answer 1

[Bruno Luong]

I'm pretty sure I answered something along this line few days ago

[m,n,p] = size(A);
[I,K] = ndgrid(1:m,1:p);
EXTRACT = A(sub2ind(size(A),I,B,K))

[heidi pham]

thank you, i just tried it and got this error: "Out of range subscript." i've searched arround but could not figure out what exactly caused this error...

[Bruno Luong]

Type

min(B(:))
max(B(:))

and verify they are with [1,n] interval, (n=30) in your case.

Answer 2

[Matt J]

[m,n,p] = size(A);
idx=reshape(B,m,1,p)==1:n;

   result=nan(m,p);
  result(any(idx,2))=A(idx);