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Tuesday, August 21, 2007

Clean Up Clean Up

Clean up.
Clean up.

Everybody everwhere.

Clean up.
Clean up.

Everybody do your share.

This is the song my wife taught our two-year old daughter in the hopes that it would make clean-up fun and encourage more of it. Sometimes it works really well and sometimes not so well. Every now and then it backfires completely and my toddler makes a big mess just so she can run around in circles singing the Clean Up song. Leaving Mommy or Daddy to do the actual cleaning.

As SAS programmers, we are given a lot of freedom to easily create as many data sets as the system will allow in the workspace. I have met many SAS programmers that do not even carry a thought about the conseqences of keeping all those work data sets hanging around. Some of the trickiest bugs to track down can be caused by stale work data sets (especially when running interactive SAS).

I have found it very useful to delete all work data sets if I am working a piece of code repeatedly. That way I make sure previous runs don't taint current runs. A simple proc datasets does the trick:

proc datasets library=work mt=data nodetails nolist KILL;

So now that you've got the song and the code, you have no excuses for leaving a mess in the work library :)

Clean up! Clean Up! Everybody Everywhere!

Tuesday, August 07, 2007

Multiple By Variables

Here is one little piece of SAS programming that I always have to work out: When using multiple "by variables" in a SAS data step, when does the grouping flip? An example:

data stuff;
set otherStuff;
by var1 var2 var3;
if first.var1 then ...;
if first.var3 then ...;

For some reason, I always have to sit and think through how multiple by variables effect each other. So here, once and for all, is the rule for me to remember:

If the group (value) changes in the variable to the left, it changes the group of all the variables on the right regardlessof their values.

It makes sense if you think it through, but sometimes it's just easier to write the rule down and refer to it (here!).

Wednesday, August 01, 2007

Summer Reading

Currently I am reading a book that is so good, I thought I would give it a quick recommendation. Against The Gods: The Remarkable Story of Risk is one of those books that I know-- before even finishing it, I will read again, and again. And I will gain deeper insights into history, humanity, stock markets, statistics and even the decisions that I make in my everyday life.

So if you get the chance, pick up a copy. And if you have any other good reads that you think I or others might be interested in, please share them here.