MATLAB: Change specific values in odd/even columns of a matrix

Question

I have a matrix and I would like to make all values which are equal x, equal to y. But I would like to do that only in odd columns. Can I do it without using a loop?

Say I have the following matrix:

>> A=randi([1,5],4,4)
A =
     5     4     5     5
     5     1     5     3
     1     2     1     5
     5     3     5     1

And I would like to turn all 1's which are in the odd columns into 0's to get the following matrix:

     5     4     5     5
     5     1     5     3
     0     2     0     5
     5     3     5     1

I tried to do the job with this code:

          A(A(:,1:2:end)==1)=0
A =
     5     4     5     5
     5     1     5     3
     0     0     1     5
     5     3     5     1

It gets the position of the 1's in the odd columns right, but it changes the values in consecutive columns instead.

I guess an equivalent question would be how to generate a logical matrix of the same dimensions of A with all values equal to 0 except these which are equal to 1 AND in odd columns.

Any ideas?

Thanks

Answer 1

Try this:

A = [5     4     5     5
     5     1     5     3
     1     2     1     5
     5     3     5     1];
L = A == 1;
L(:,2:2:end) = false;
A(L) = 0

producing:

A =
     5     4     5     5
     5     1     5     3
     0     2     0     5
     5     3     5     1