function-style array indexing

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

Answer 1

[Walter Roberson]

idxcell = repmat({':'}, 1, ndims(A));
idxcell{n} = ii;
A(idxcell{:})

[Daniel Shub]

This is the exact recommendation in Loren's blog.

[Ben Mitch]

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)?