Dimension-wise logical indexing in a 3D array

Question

Say I have an array stack of dimensions NxMxR. I would like to use logical indexing on a given dimension to update its value, without the use of a temporary variable.

Example using the temporary variable:

for k=1:R
    temp=stack(:,:,k);
    temp(temp<max(max(temp))/2)=NaN;
    cropped(:,:,k)=temp;
end

Note that it would be trivial if the condition was the same for the entire array, but it varies along the R dimension. bsxfun would be appropriate if I just wanted to subtract the threshold value in a syntax like:

cropped = bsxfun(@minus, stack, max(max(stack, [], 3))/2);

I find the use of the temporary variable clumsy and can't find a proper way of defining the function for bsxfun to do what the loop does.

Does anyone has a suggestion?

Answer 1

stack(bsxfun(@minus, stack, max(max(stack))/2) < 0) = NaN;