efficiently modifying a 0-1 matrix for a fixed row sum

[Mike B.]

Hi All,

I have a matrix of 0-1 elements which are randomly distributed.

I need to modify the matrix such that each row has exacly the same sum, for 
example, assuming the target sum is 2 and the initial matrix is
0 1 0 (sum=0, too low)
1 1 1 (sum=3, too high)

one possible outcome is
1 1 0 (sum=2)
1 0 1 (sum=2)

Any way to avoid slow for loops?.

Thanks,
Mike.