Using Nx1 vector as index to extract values from an NxM matrix and create an Nx1 vector

Hi. I will try to explain my title:

I have an NxM matrix, e. g.

M = [1 2 3; 4 5 6; 7 8 9];

and an Nx1 index vector, e. g.

I = [2; 3; 1];

I would like to create a vector V using I as an index for M to extract values from M so that

V(i) = M(i,I(i))

without using a loop, if possible.

So the resulting vector V in this example would result as:

V = [2; 6; 7];

Thanks for any help or hints!

Answer 1

[Star Strider]

Use the sub2ind function to create a linear index:

M = [1 2 3; 4 5 6; 7 8 9];
I = [2; 3; 1];
J = sub2ind(size(M), [1:3]', I);
V = M(J)

produces:

V =

       2
       6
       7

[Marc Jakobi]

Thanks!

[Star Strider]

My pleasure!