accessing indexed values in a 3D array

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Chad Greene
Chad Greene 2015-7-27
评论： Chad Greene 2015-7-27
I have a 3D array of temperature data that looks like this:
Z = rand(3,4,8);
It contains 8 slices of data on a 3x4 grid. For each point in the 3x4 grid I have an index that correspond to a slice the third dimension:
ind = randi(8,[3 4])
How do I create a 3x4 surface of values in Z given by the indices ind? I could do it manually like this:
s(1,1) = Z(1,1,ind(1,1));
s(1,2) = Z(1,2,ind(1,2));
s(1,3) = Z(1,3,ind(1,3));
...
s(3,4) = Z(3,4,ind(3,4));
But my Z matrix is 500x500x100, so doing it manually is out of the question. I'm sure I can avoid a loop here somehow.

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采纳的回答

David Young
David Young 2015-7-27
[rows, cols] = ndgrid(1:size(Z,1), 1:size(Z,2));
Zindex = sub2ind(size(Z), rows, cols, ind);
s = Z(Zindex);

更多回答（1 个）

Walter Roberson
Walter Roberson 2015-7-27
Zs = size(Z);
S = zeros(Zs(1), Zs(2));
ind_offset = (ind - 1) * Zs(1) * Zs(2) + (1:numel(S));
S(1:numel(S)) = Z(ind_offset);
  2 个评论
Walter Roberson
Walter Roberson 2015-7-27
I made a mistake in the above. Also after seeing David's perfectly workable answer I would improve mine:
Zs = size(Z);
ind_offset = (ind - 1) * Zs(1) * Zs(2) + reshape(1:Zs(1)*Zs(2),Zs(1),Zs(2));
S = Z(ind_offset);

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