Select elements of a matrix using an array (of indices)

Hi, I have a matrix composed of 2 columns, called A, and an array of "indices", called I.

For each row of A, I would like to select the element in the first or in the second column, according to the number, 1 or 2, contained in the array I. This means, if I have the number 1 in the array I, I would select the element in the first column of A. Viceversa, if I have the number 2 in the array I, I would select the element in the second column of A.

It is a very silly question, but can I select the elements of A, just using I as indeces, instead of a loop ?

Something like this ?

B = A(:,I)

This is my example:

% Input

A =

         164         101
        2733        2801
         323         410
          20          24
         556         494
         498         345
          59         246
         394         341
         873         870
         627         702
         923        1027
         109         106

I =

     1
     2
     2
     2
     1
     1
     2
     1
     1
     2
     2
     1
     
% Desired Output

B' =

         164
        2801
         410
          24
         556
         498
         246
         394
         873
         702
        1027
         109
         
% Note: I used this loop to get B, but I would like to avoid it, and use something like B = A(:,I)

for i = 1 : size(A,1)
    B(i) = A(i,I(i));
end

Answer 1

[Bruno Luong]

A=[164         101
    2733        2801
    323         410
    20          24
    556         494
    498         345
    59         246
    394         341
    873         870
    627         702
    923        1027
    109         106];
I =[1
    2
    2
    2
    1
    1
    2
    1
    1
    2
    2
    1];
B = A(sub2ind(size(A), (1:size(A,1))', I(:)))'

B = 1×12

164 2801 410 24 556 498 246 394 873 702 1027 109

[Sim]

Thanks a lot @Bruno Luong!!

Would it be possible to use the same solution you have proposed when I have zeros in A and in I ?

Indeed, if I have some zeros in both A and I, I get the following error:

% Input

A =[       0           0
        3850        3886
           0           0
           0           0
           0           0
           0           0
           0           0
           0        3856
           0           0
           0           0
           0           0
           0           0
           0           0
           0           0
           0           0
           0           0
           0           0
           0           0
           0           0
        3887        3831
           0           0
           0           0
           0           0
           0           0
           0           0
           0           0
           0           0
        3879        3812
        3878        3847
        3796        3885
           0           0];
           
I =[ 0
     1
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     2
     0
     0
     0
     0
     0
     0
     0
     2
     2
     1
     0];

B = A(sub2ind(size(A), (1:size(A,1))', I(:)))'
     
% Output

Error using sub2ind (line 55)
Out of range subscript.

Error in untitled2 (line 66)
B = A(sub2ind(size(A), (1:size(A,1))', I(:)))'

[Bruno Luong]

No MATLAB is 1-based indexing.

[Sim]

ah ok, many thanks!!