function-style array indexing

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Ben Mitch
Ben Mitch 2013-3-13
编辑： per isakson 2016-8-5
Hi
This problem keeps coming up for me over the years, and there must be a standard solution, so perhaps someone knows it, I can't ever google it up.
Say I have an array A of any number of dimensions, and I want to apply an indexing operation to the last dimension. Now, if it's 2D, I just use:
B = A(:, ii);
If it's 3D, I use:
B = A(:, :, ii);
but what if it's n-D? Afaik there is no syntax in the language for this, so I'd have to use some function. A function "index_into()", for instance, to give:
B = index_into(A, n, ii);
At the moment, I always end up doing some horrible mash like:
X = permute(A, [ndims(A) ...]);
X = X(ii, :);
X = reshape(X, ...);
B = permute(X, ...);
Surely there must be a better way...? Any suggestions?
Cheers

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采纳的回答

Walter Roberson
Walter Roberson 2013-3-13
idxcell = repmat({':'}, 1, ndims(A));
idxcell{n} = ii;
A(idxcell{:})
  2 个评论
Daniel Shub
Daniel Shub 2013-3-13
This is the exact recommendation in Loren's blog.
Ben Mitch
Ben Mitch 2013-3-13
Nice, thanks. I think I had seen that index-by-comma-separated-list before, but it hadn't taken root in my mind. Wonder, though, if a syntax would be possible that made this a bit more intuitive. Just curious...
A(..., ii)?

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