Technology Tales

Dealing with variable length warnings in SAS 9.2

11th January 2012

A habit of mine is to put a LENGTH or ATTRIB statement between DATA and SET statements in a SAS data step to reset variable lengths. By default, it seems that this triggers truncation warnings in SAS 9.2 or SAS 9.3 when it didn’t in previous versions. SAS 9.1.3, for instance, allowed you have something like the following for shortening a variable length without issuing any messages at all:

data b;
length x $100;
set a;
run;

In this case, x could have a length of 200 previously and SAS 9.1.3 wouldn’t have complained. Now, SAS 9.2 and 9.3 will issue a warning if the new length is less than the old length. This can be useful to know but it can be changed using the VARLENCHK system option. The default value is WARN but it can be set to ERROR if you really want to ensure that there is no chance of truncation. Then, you get error messages and the program fails where it normally would run with warnings. Setting the value of the option to NOWARN restores the type of behaviour seen in SAS 9.1.3 and versions prior to that.

The SAS documentation says that the ability to change VARLENCHK can be restricted by an administrator so you might need to deal with this situation in a more locked down environment. Then, one option would be to do something like the following:

data b;
drop x;
rename _x=x;
set a;
length _x $100;
_x=strip(x);
run;

It’s a bit more laborious than setting to the VARLENCHK option to NOWARN but the idea is that you create a new variable of the right length and replace the old one with it. That gets rid of warnings or errors in the log and resets the variable length as needed. Of course, you have to ensure that there is no value truncation with either remedy. If any is found, then the dataset specification probably needs updating to accommodate the length of the values in the data. After all, there is no substitute for getting to know your data and doing your own checking should you decide to take matters into your hands.

There is a use for the default behaviour though. If you use a specification to specify a shell for a dataset, then you will be warned when the shell shortens variable lengths. That allows you to either adjust the dataset or your program. Also, it gives more information when you get variable length mismatch warnings when concatenating or merging datasets. There was a time when SAS wasn’t so communicative in these situations and some investigation was needed to establish which variable was affected. Now, that has changed without leaving the option to work differently if you so do desire. Sometimes, what can seem like an added restriction can have its uses.