Selecting Elements of a Matrix by Indexing with a Vector

I have a 100x3 matrix and I'd like to select one element from each row to form a 100x1 vector. Given a vector of 100 indeces between 1-3, how can I obtain this? The code below is what I thought should work, but instead produces a 100x100 matrix (concatenation of each 100x1 vector generated by each value of indx).

A = rand(100,3);
indx = randi([1 3],100,1); % for each row, which column do I want to pull the element from?
B = A(:,indx); % B is 100x100, I want 100x1

Answer 1

[Ameer Hamza]

See sub2ind() function.

A = rand(100,3);
indx = randi([1 3],100,1);
idx = sub2ind(size(A), (1:size(A,1)).', indx);

B = A(idx);

[Darren Wethington]

This worked, I was just hoping to not have to sub2ind it and was curious if there was a more straightforward way. I'll use this, thanks.

[Ameer Hamza]

I think sub2ind is the simplest way to do such a thing. Following avoids sub2ind, but I am not sure you can call it straightforward

A = rand(100,3);
indx = randi([1 3],100,1);
ind =  (1:size(A,1)).' + (indx-1).*size(A,1);

B = A(ind);

Answer 2

[David Hill]

A = rand(100,3);
indx = randi([1 3],100,1);
B = A(1:100,indx); 

[Darren Wethington]

This did not work for me, I thought it should.