Understand the _IORC_ Automatic Variable in SAS

Last week, I blogged about the well-known automatic variable in the SAS Data Step: The _N_ Variable. Today, the topic will be another automatic variable in the data step, though not as famous. Today’s topic is the _IORC_ automatic variable. Never heard of  it? Fear not. Not many SAS programmers have. In this post, i will introduce the variable, show you where programmers commonly uses it and why.

A Small Introduction

IORC stands for Input Output Return Code. The _IORC_ variable is commonly used in conjunction with a Modify Statement or a Set Statement where the Key= Option is used on a SAS Data Set Index. In this context, SAS returns a numeric value to the _IORC_ variable, which indicates whether the Index search was successful or not. You can see a classic example in the blog post Using the Modify Statement in the SAS Data Step.

However, _IORC_ is not limited to this situation. Even though the SAS Documentation lists only two automatic variables in the data step, the _IORC_ variable is present even SAS does not perform an index search. Take a look at this small code example

data test1;
	set sashelp.class;
	put _IORC_=;
run;

Here, I simply read the sashelp.class data set. Despite the fact that I use no indexes, the _IORC_ variable is available for us to put in the log.

Four Facts to Understand the _IORC_ Variable

Now, to understand the _IORC_ variable, let me list a few rules of thumb to better understand it. SAS

  1. Automatically drops the _IORC_ variable.
  2. Initializes _IORC_ with a zero value.
  3. Automatically retain the variable
  4. Does not change the value of _IORC_ unless it performs an index search

Rule 1 and 2 above are easy to verify. If you check the log from the small code snippet, you can see that _IORC_=0. Furthermore, the variable is automatically dropped. This is no surprise. Rule 3 may surprise you though. Take a look at the code snippet below

data test2;
	set sashelp.class;
	if _N_=5 then _IORC_=1;
	put _IORC_=;
run;

When you check the log you can see that when we change the value of _IORC_ this value stays intact until we change it again. This is in contrast to the _N_ variable, which is changed every time the data step iterates through the Data Statement. This brings us to rule 4. SAS does not change the value of _IORC_ unless you do so yourself or an index search is performed. This makes the _IORC_ variable usable in other contexts than the _N_ variable because we know that in most circumstances, _IORC_ is zero by default, retained and untouched by SAS.

Summary

So should we use the _IORC_ variable more? Well, it depends. The _IORC_ variable is commonly used among advanced SAS programmers when a temporary, retained variable is needed. For example as a return code for a Hash Object Search, the variable is popular. Browsing the SAS Community, you will see many examples of using the _IORC_ variable. Though we can recode all of them with a regular variable, a retain statement and a drop statement. There is nothing magic about the _IORC_ variable that can not be replicated. One could even argue that the code looks messier and that other coders may have a harder time understanding your code.

I encourage you to browse the community and see where programmers use the _IORC_ variable. Take a look at the slick example here for example. Also, you can read about another non familiar automatic variable in the post Implicit and Explicit Arrays in SAS.

You can download the entire code from this post here.