Substract nd array slices
显示 更早的评论
Hi,
I have a n-dimensional array which may contain singleton dimensions and I would like to substract the second page of dimension i from the first page of dimension i. My current solution looks something like this:
function A = substract_page( A, dim )
orig_size = size(A); % store the original shape
A = shiftdim(A, dim); % shift the dimension to be substracted to the end
shifted_size = size(A); % aliter: shifted_size = circshift orig_size(dim); ?
A = reshape(A, [], shifted_size(end)); % collapse first dimensions for easier substraction
A = A(:, 2) - A(:, 1);
shifted_size(end) = shifted_size(end) - 1; % substraction leads to dimension loss
A = reshape(A, shifted_size); % restore shape
lost_dimensions = length(orig_size) - ndims(A);
A = shiftdim(A, -lost_dimensions); % make sure that singular dimensions in the end don't get lost
A = shiftdim(A, length(orig_size) - dim + lost_dimensions); % restore order
end
But it seems way to complicated and I feel there is a much easier and more elegant solution.
采纳的回答
Does your code perform this:
dim = 3;
A = rand(2,3,4,5);
A = A(:, :, 2, :) - A(:, :, 1, :)
? Then:
function A = substract_page(A, dim)
C1 = repmat({':'}, 1, ndims(A));
C2 = C1;
C1{dim} = 1;
C2{dim} = 2;
A = A(C2{:}) - A(C1{:});
end
3 个评论
Orangelynx
2017-11-13
Jan
2017-11-13
@Orangelynx: When the dimension to operate on has the length 2, diff is perfect. My code would be useful only, if the input has e.g. the length 4 as in my example, and only the difference between the first 2 slices should be calculated ignoring the rest.
Orangelynx
2017-11-13
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