How can I extract a slice from a multidimensional array?

I have an array of variable dimensions and want to extract a slice of it.

If I the size of the array was fixed I would like to do:

result = G(:,:,:,r,:,:);

But in my case, r is a variable and so are the dimensions of G and the dimension from which I want to extract the slice (in this case the 4th dimension).

-----------------------------------

I am able to costruct a cell array containing the indices that need to be extracted, but can't extract them.

N = ndims(G);

other_dimensions = [1:(n-1),(n+1):N];

sz = size(G);

inds = repmat({r},1,ndims(G));

for k = 1:length(other_dimensions)

inds{other_dimensions(k)} = 1:sz(other_dimensions(k));

end

result = A(inds) % (not working)

Answer 1

[Stephen23]

The trick here is to define a cell array and then use a comma-separated list for the indices. For example:

G = rand(7,6,5,4,3,2); % any size
d = 4; % which dimension
r = 3; % index in that dim.
% define cell array:
C = repmat({':'},1,ndims(G));
C{d} = r;
% comma-separated list to supply indices:
S = G(C{:}); % get slice!
% check:
size(G) % original array

ans = 1×6

7 6 5 4 3 2

size(S) % slice

ans = 1×6

7 6 5 1 3 2

isequal(S,G(:,:,:,r,:,:))

ans = logical
   1

https://www.mathworks.com/help/matlab/matlab_prog/comma-separated-lists.html

https://www.mathworks.com/matlabcentral/answers/320713-how-to-operate-on-comma-separated-lists

[Uri Goldsztejn]

Thank you for your answer! I realized I could change 1:sz(other_dimensions(k)) for ':' in my code and solve the problem as well. I.e.,

N = ndims(G);

other_dimensions = [1:(n-1),(n+1):N];

sz = size(G);

inds = repmat({r},1,ndims(G));

for k = 1:length(other_dimensions)

inds{other_dimensions(k)} = ':';

end

result = A(inds) % (now it works)