Get list of values of matrix from indices list in Matlab

Question

I have a matrix like this:

A = [35,  1,   6,  26;
     3,   32,  7,  21;
     31   9,   2,  22;
     8,   28,  3,  17];

and a list of indices like this:

B = [1,  1;
     1,  2;
     2,  2;
     1,  3];

I want to get list of values from matrix A with indices in B

C = [35, 1, 32, 6]

I use this code:

C = A(B==1)

But the C is :

[35, 3, 8, 1]

Where am I wrong?

Answer 1

You can use sub2ind to convert your row,col indexing to linear indexing.

A = [35,  1,   6,  26;
     3,   32,  7,  21;
     31   9,   2,  22;
     8,   28,  3,  17];

B = [1,  1;
     1,  2;
     2,  2;
     1,  3];

linear_ind = sub2ind(size(A), B(:,1), B(:,2));
C = A(linear_ind)

Which will result in

C =
    35
     1
    32
     6