Comparison operator in SAS – The =: Operator

Most people familiar with programming SAS know the colon operator ( =: ). There are a couple of different colon operators in SAS. However, in this post, I’m only talking about the comparison operator in SAS. The equal colon operator works very similarly to the substr() function. It is used to compare substrings for equality.

Here is a quick little example:

data null;  
x = 'abcdefg';  
if x =: 'abc' then put 'The substrings match.'; 
run;

As you may see when you run, the data step above the substring ‘abc’ matches in ‘abcdefg’.

A better way to think about it is to ” start with” the substring. This statement could also achieve the same:

if substr(x,1,3) = 'abc'  then put 'The substrings match.';

There is one major difference between the =: operator and using substr().

With the substr() function, you tell SAS precisely how many characters to search for the substring.

In the example above, it was 3. For the =: operator, it must determine the number of characters to look for.

data null;  
x = 'abcdefg';  
if x =: 'abc' then put 'The substrings match.'; 
run;

You will notice that they match if you run the above data step..It appears to be slightly humorous because most of us assume that SAS is searching for ‘abcdefg’ within ‘abc’. However, that is probably not what’s happening.

SAS uses the shortest string to determine what to search for, irrespective of which side of the equals signal it’s on.

Oh yeah, the =: operator additionally works in a list context similar to:

if x in: ('abc', 'xyz', 'def');