The other day I needed to compute the signum function for each element of a matrix. If x is a real number, then the sgn(x) is -1 when x<0, 1 when x>0, and 0 when x=0.

I wrote a SAS/IML module that contains a compact little expression:

proc iml;
start sgn(x);
   return( (x>=0) - (x<=0) );
finish;

However, even before I tested the function, I heard a little voice inside my head calling "I'll bet SAS already has this function...." A short search later, and I had discovered the built-in SIGN function:

x = {-3 2  0,
      5 0  7,
     -2 1 -5 };
s = sign(x);
print s;

Lessons learned:

• You can call Base SAS functions from the SAS/IML language and apply the results to each element of a matrix.
• SAS is a huge language. There is always something new to learn.