MATLAB: How to pull out indicies from a matrix

Question

I have a matrix which is essestially two vectors. It looks something like:

Row 1: 1,2,1,2,1,2,1,2,1,2………

Row 2: 132.2, 132.7, 133.5………..

I want to pull out the indexes that correspond under all of the ones and twos into another vector. I've done something like:

A(A ==1) so it pulls out all of the 1s, but I want it to pull the values in the row underneath the 1 as well.

Answer 1

Let A be your 2*m matrix...

r1 = A(1,:) ;
r2 = A(2,:) ; 
iwant = r2(r1==1)
iwant = r2(r1==2)

From matrix directly.

iwant = A(:,A(1,:)==1)
iwant = A(:,A(1,:)==2)