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Picking values from n-d array along 3rd dimension

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Pal
Pal 2013-6-11
Hi,
Suppose I have A, an m x n x q array with large integer values.
I have B, an m x n array of integer values in the range of 1:q.
I'd like to pick values from A along the 3rd dimension, so that I obtain C, an m x n array in which for every subscript pair (i,j), m>i>1, n>j>1 the following is true:
x = B(i,j)
C(i,j) = A(i,j,x)
Is there an efficient, loop-free way of doing this?
Many thanks,

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采纳的回答

Andrei Bobrov
Andrei Bobrov 2013-6-11
编辑：Andrei Bobrov 2013-6-11
[ii,jj] = ndgrid(1:m,1:n);
ijk = sub2ind(size(A),ii,jj,B);
C = A(ijk);

更多回答（2 个）

Roger Stafford
Roger Stafford 2013-6-11
C = A((1:m*n)'+m*n*(B(:)-1));
C = reshape(C,m,n);
David Sanchez
David Sanchez 2013-6-11
You can assign the value of C without referencing (i,j):
x = B(i,j);
C = A(:,:,x);
And you will have for all i, j that C(i,j) = A(i,j,x)
  1 个评论
Pal
Pal 2013-6-11
Could you elaborate, please? If I write
C = A(:,:,B),
the answer is an m x n x numel(B) array, which is incorrect. What do you mean by 'without referencing (i,j)'? B is not constant.

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