How do I index an array with varying dimension?

I have a function Y = func(X)

X can be any dimension >=2. Inside the function, I need to index X by the first dimension. X(index, :) or X(index, :, :) depending on the dimension. I know I can check the dimension like this:

if ndims(X) == 2

X(index, :) = ....

elseif ndims(x) == 3

X(index, :, :) = ..

end

Is there a more efficient way?

[Stephen23]

"Is there a more efficient way?"

https://www.mathworks.com/matlabcentral/answers/1656435-tutorial-comma-separated-lists-and-how-to-use-them#answer_902595

Answer 1

[Walter Roberson]

If you use a trailing dimension of : to index, then the result has the proper size but with the dimension "unwrapped"

A = ones(3,4,5);
B = A(2,:);
size(B)

ans = 1×2

1 20

You can leave it like that for computations, or you can reshape() it

sz = size(A);
sz(1) = 1;
C = reshape(B,sz);
size(C)

ans = 1×3

1 4 5

Alternately....

indx = repmat({':'}, 1, ndims(A));
indx{1} = 2;
D = A(indx{:});
size(D)

ans = 1×3

1 4 5