Monday 8 February 2010

NOTE: More on IFC and IFN

It seems my recent post on the IFC and IFC functions caused a fair bit of interest. Not least in further related functions.

Firstly I must own-up to my mistake of originally stating IFC and IFN were new with 9.2. A number of correspondents pointed-out that they were available from the beginning of V9. Plus, I have it on good authority that they were experimental in V8.2 (albeit possibly with different names). They were implemented primarily to provide a logical construct that could be used interchangeably in both SQL and data step code. They happen to be a lot shorter than SQL's case/when/else construct too! My thanks to the little ex-SAS birdie and the correspondent who passed the message along.

Secondly, The SAS Plumber started a thread on In response, Data _Null_ pointed-out that the third conditional value only gets returned when the value of the first parameter is actually missing; hence my description of the functionality was incorrect. Jason Secosky pointed-out the same thing in comments on the original post. And Ron Fehd highlighted the safe, traditional option of using the SELECT statement.

Finally, Jack Hamilton suggested a look at CHOOSEC and CHOOSEN. These were new to me too - I've clearly been walking around with my eyes closed (and bumped into something, causing the poor quality of the original IFC/IFN post!). The syntax for both is:

CHOOSEx (index-expression, selection-1 <,...selection-n>)

The CHOOSEx function uses the value of index-expression to select from the arguments that follow. For example, if index-expression is three, CHOOSEx returns the value of selection-3. If the first argument is negative, the function counts backwards from the list of arguments, and returns that value.

In his comments to the original posting, Jack also mentioned that IFC/IFN are also available in the macro language via %SYSFUNC, and so provide a primitive IF/THEN/ELSE mechanism in open code. Jack highlighted the example in the wiki.

So, I now know four functions that I'd not heard of just a few short weeks ago. And I've made a note to read the documentation more carefully before posting next time! My thanks to all of you who contributed to the discussion.