How to specifically select columns from a matrix?

Dear All,

For a given 2 columns matrix A. For example

Can I extract the first 3 elements in the 2nd columns and the 4th and 5th elements in the first column by one commend?

I tried the following way but failed: First, I defined an array as follows,

Then I did A(:,r) and it did not work.

Thanks a lot. Bei Gou

Answer 1

[Stephen23]

>> A = [1,2;3,4;5,6;7,8;9,10]
A =
    1    2
    3    4
    5    6
    7    8
    9   10
>> R = [1,2,3,4,5];
>> C = [2,2,2,1,1];
>> X = sub2ind(size(A),R,C); 
>> A(X)
ans =
   2   4   6   7   9