Accessing certain Dimension of Multidimensional Array

Hi All,

Recently I've been working on a problem where I have a multidimensional array where I don't know how how many dimensions I have, but I want to get all the items that are in the ith slice (row, column, matrix, hyperplane, idk what to call it) of the jth dimension. Is there any way to do this easily in MATLAB?

As an example, for a 3x3x3 matrix, if I want the 2nd slice in the 3rd dimension, I wold go A(:,:,2), but here I don't have the luxury of typing however may semicolons I want.

Answer 1

[Matt Fig]

Here is how I would do it:

% A is given, up to 8 dims here.
A = rand(max(2,randi(4,1,max(3,randi(8))))); 

idx1 = 2;                 % Say we want the idx1th slice of 
idx2 = randi(ndims(A));   % The idx2th dimension.
C = repmat({':'},1,ndims(A));
C(idx2) = {idx1};  %This is our index into A.
SLC = A(C{:})  % Here is our slice.

[Azzi Abdelmalek]

Very good answer! I like it

[Matt Fig]

Thanks, Azzi! The first time I saw a cell array used to index a numeric array this way was Walter showing someone how to do it 2-3 years ago. That Walter knows all the tricks!

Answer 2

[Matt J]

Just because I'm fond of circumventing repmat :-)

i=2, %slice
j=3; %dim

S=size(A);
Ar=reshape(A,prod(S(1:j-1)),[], prod(S(j+1:end)));

slice = reshape( Ar(:,i,:) , [S(1:j-1), 1, S(j+1:end)]);