Return a vector with the same size as the indexing matrix/vector (code optimization)

I have the following problem:

I would like to access elements inside a vector (in this case, a vector column) and avoid the use of any loops.

The output of the vector can have a different ordering, given the values of the index matrix.

When i have a vector column like

V=[20;10;13] , then the size is (size(), m=3,n=1)

Therefore, when i access it with a matrix like index = [1 3;2 1]

V(index) returns a matrix of (size(),m=2,n=2)

Nevertheless, when the index is a matrix with a single row (or row vector), the output is a column vector (instead of the desired row vector)

index = [1 3]

V(index) returns a matrix of (size(),m=2,n=1) instead of returning the desired (size(),m=1,n=2)

Anyone knows how I could solve this? (My software could have an index matrix with 1 or more rows)

Answer 1

[Rik]

I would have expected Matlab to have consistent behavior, but before now I hadn't bothered to look it up in the documentation. You can revert a possible flip by using reshape:

V=[20;10;13];
index=[1 3;2 1];
out=reshape(V(index),size(index))

Answer 2

[Andrei Bobrov]

General case:

out = reshape(V(index),size(index));

For your case V - vector (n x 1):

if size(index,1) == 1
    out = V(index)';
else
    out = V(index);
end