topic Re: nested if-then/else grouping in SAS Procedures

nested if-then/else grouping

CharlesR — Thu, 15 Jul 2010 03:56:46 GMT

Hello,
I've got the following if-then/else data grouping.

[
if Runner3BId=0 then
_if Runner2BId=0 then
___if Runner1BId=0 then do;
_______baserunners = 0; /*bases empty*/
_________end;
_______else do; baserunners = 1; /*man on 1b*/
_______end;
__else if Runner2BId ^= 0 then do;
____yada, yada
end;
] this part works fine and assigns the baserunners variable correctly

but the second half of the Runner3BId has the correct nesting structure but doesn't assign the variable. so the problem has to be in the first 2 line here (i think) but for the life of me, i can't see what is wrong.
[
_else if Runner3BId ^= 0 then do;
__if Runner2BId=0 then
_____if Runner1BId=0 then do;
________baserunners = 3; /*man on 3b*/
________end;
_____else do; baserunners = 5; /*men on 1b&3b*/
_____end;
__else if Runner2BId ^= 0 then do;
yada, yada
__end;
_end;
run;
]

Anyone see what i'm doing wrong?

damn it, why don't they allow the leading spaces on the lines? let's try underscore Message was edited by: CharlesR

Re: nested if-then/else grouping

ieva — Thu, 15 Jul 2010 07:00:40 GMT

It is very hard to read your code and understand if-then logic there. One thing – maybe instead of

if Runner2BId=0 then
if Runner1BId=0 then do;

you should write

if Runner2BId=0 and
if Runner1BId=0 then do;

And maybe you should check the logic of the code – where does do-end start and end, maybe code is skipping some important part.

Good luck in fixing your code!

Re: nested if-then/else grouping

deleted_user — Thu, 15 Jul 2010 14:19:41 GMT

also the sequencing of if-then statement.

if 'condition1' then do ; .... end;
else if 'condition2' then do ; .... end;
else if 'condition3' then do ; .... end;
.
.
.
.
else do; .... end;

Re: nested if-then/else grouping

sbb — Thu, 15 Jul 2010 14:28:13 GMT

Also, for diagnosing your own SAS program, consider using PUTLOG _ALL_; and/or issue a PUTLOG command with a unique text-message in one or more of your DO/END code paragraphs.

Scott Barry
SBBWorks, Inc.

Re: nested if-then/else grouping

CharlesR — Fri, 16 Jul 2010 03:15:21 GMT

i thought about a simple
but it also didn't work.

Re: nested if-then/else grouping

sbb — Fri, 16 Jul 2010 04:18:03 GMT

Your attempts to use nested/stacked IF / THEN without using an associated DO/END is causing your code path to fail. Suggest you simplify your code by using complete DO/END structure for all code paths, even if only one line of code.

Scott Barry
SBBWorks, Inc.

Re: nested if-then/else grouping

CharlesR — Fri, 16 Jul 2010 04:25:15 GMT

I'm not sure i totally understand what you're saying. i'd like to think that i understand, but, i'd be wrong, lol.

what is an associated DO/END? specifically, how is it different from what i have done so far?

Re: nested if-then/else grouping

sbb — Fri, 16 Jul 2010 12:54:09 GMT

You have a hierarchy of IF THEN ; and attempting to use that structure also with nested ELSE/DO/END and/or ELSE IF THEN code paragraphs, intermixed. Because of your coding technique, those nested logic paths may or may not fire (based on your logic) and by using DO/END for each of the nested code path conditions, you will see more predictable code execution. Also, for your own debugging, by using the DO/END logic, you can then insert PUTLOG commands to more easily test all logic paths, where messages get echo'd to the SASLOG.

Scott Barry
SBBWorks, Inc.

Re: nested if-then/else grouping

CharlesR — Fri, 16 Jul 2010 14:26:20 GMT

Ah. I'm quite new to SAS and was somehow under the impression that my IF/THEN loop had to have the DO statement in order to work.

So i can essentially write a series of DO loops which will assign the values correctly. I would then assume i have to have the data sorted appropriately, meaning sorted by Runner3BId, Runner2BId, Runner1BId. i could essentially have something like this:

do until(EndoFile);
__do until Runner3BId ^= 0;
___do until Runner2BId ^= 0
_____do until Runner1BId ^= 0;
_______baserunners = 0; /*bases empty*/
_____END;
_____baserunners = 1; /*man on 1st*/
___END;

etc. etc.

Re: nested if-then/else grouping

sbb — Fri, 16 Jul 2010 14:35:37 GMT

Uhhh, you're going to need a SET statement somewhere inside the outer DO/END loop, and I suggest exploring the use of LEAVE and CONTINUE, as well, depending on your circumstances. Also, the STOP; statement possibly for premature DATA-step termination.

Although, you also need to understand about SAS DATA step pass behavior when running a DO/END with an interior SET statement -- effectively you only execute one DATA step pass (depends on the application rqmt though).

Scott Barry
SBBWorks, Inc.

Suggested Google advanced search argument, this topic / post:

data step programming intro site:sas.com

Re: nested if-then/else grouping

Peter_C — Fri, 16 Jul 2010 14:41:28 GMT

CharlesR

although you are new to SAS you may not be new to such IF/THEN logic.
To watch the data step flow, I would really recommend using the data step option /DEBUG ; [pre]data output_data_set /debug ;
do whatever ;
if whatever ........ ;
end ;
run ;[/pre]
Debugger will let you step through your code and examine variable values - but does not work in SAS Enterprise Guide - yet.

good luck
peterC

Re: nested if-then/else grouping

CharlesR — Fri, 16 Jul 2010 17:18:52 GMT

i am doing this all under data, so it begins with

data testdata;
__set testdata;

then goes into the do loop.

as for leave and continue, the problem with them is that they will exit the loop correct? i note how you say depending on the circumstances, the biggest problem is that i'm not sure how to incorporate them when i want the loop to cycle through all the data.

also, how can i sort the data in a binary fashion? i.e. i want it to sort by Runner3BId as to whether it = 0 or is > 0, then within that as to whether Runner2BID is = 0 or >0 and then the same with Runner1BId, as opposed to everything running numerically. Am i better off simply creating a new variable which simply indicate whether there is someone on 1st, 2nd and/or 3rd?

Re: nested if-then/else grouping

sbb — Fri, 16 Jul 2010 17:29:13 GMT

Numeric variables yield a binary sort or if you are more concerned, yes, detect some condition and set a 1 or 0, and sort on that as a BY variable.

And, so, if you do not want to exit a DO/END loop, use some combination of variables in an expression, to get you into the loop and then set a flag-variable to get you out.

Scott Barry
SBBWorks, Inc.

Re: nested if-then/else grouping

CharlesR — Fri, 16 Jul 2010 19:15:17 GMT

Where can i find how to do a binary sort with numeric values? Tried to google it, but not sure where to look exactly . . .

Re: nested if-then/else grouping

sbb — Fri, 16 Jul 2010 19:36:26 GMT

Honestly, you should open a new forum thread...

Start here with basic SAS PROC SORT documentation, then review the particulars for your OS with the SAS Companion guide.

Google advanced search argument, this topic / post:

proc sort documentation site:sas.com

proc sort numeric variables binary collation site:sas.com

numeric variables binary collation sort site:sas.com

Scott Barry
SBBWorks, Inc. Message was edited by: sbb

Re: nested if-then/else grouping

Cynthia_sas — Fri, 16 Jul 2010 23:54:26 GMT

I'm responding to this statement:

Ah. I'm quite new to SAS and was somehow under the impression that my IF/THEN loop had to have the DO statement in order to work.

Here's the deal....Let's start with a simple IF statement and a simple IF/ELSE:
[pre]
if wombat = 'true' then < put 1 and only 1 statement here > ;

OR

if wombat = 'true' then < put 1 and only 1 statement here > ;
else < put a single statement here > ;
[/pre]

The very nanosecond that you say to yourself...oh gosh, I need to have 2 or 3 statements get executed if wombat = 'true' then you are into the world of the DO/END block (or as we used to say in my programming class -- the structured IF/DO/END):
[pre]
if wombat = 'true' then do;
< put 1 statement here > ;
< put statement 2 here > ;
< put statement 3 here > ;
end;

OR

if wombat = 'true' then do;
< put 1 statement here > ;
< put statement 2 here > ;
< put statement 3 here > ;
end;
else do;
< put diff statement 1 here > ;
< put diff statement 2 here > ;
< put diff statement 3 here > ;
end;

OR, even -- transmute the simple IF to an IF/DO/END:

if wombat = 'true' then do;
< put 1 and only 1 statement here > ;
end;
else do;
< put a single statement here > ;
end;
[/pre]

In fact, my SAS mentor was something of a curmudgeon about NOT using the simple form of the IF statement -- on the a theory that if you used the IF/DO/END construction, even when you only needed to execute 1 statement on the true and another single statement on the false -- it would be easier for you maintenance-wise and in the long run (when you had to modify the code to add more statements) to just have the DO/END used all the time. Then it was easy to document:
[pre]
if wombat = 'true' then do; /* when wombat is true, set foobar to 1 */
< put 1 and only 1 statement here > ;
end; /* end wombat true */
else do; /* when wombat is false, set foobar to 0 */
< put a single statement here > ;
end; /* end wombat false */
[/pre]

Now that may seem overkill in the documentation department but consider the nested DO possibilities:
[pre]
if wombat = 'true' then do; /* when wombat is true, set foobar to 1 */
< put 1 and only 1 statement here > ;
if character = 'kermit' and street = 'sesame' then do; /* kermit test */
< put 1 statement here > ;
< put statement 2 here > ;
end; /* end for kermit test */
end; /* end wombat true */
else do; /* when wombat is false, set foobar to 0 and test character and hat*/
< put a statement here > ;
if character = 'tom terrific' and hat = 'pointed' then do; /* tt and hat test */
< put 1 statement here > ;
< put statement 2 here > ;
end; /* end tom terrific and hat test */
else do; /* do not care about any other character */
< put a statement here > ;
end; /* end for tom terrific when wombat is false */
end; /* end wombat false */
[/pre]

and I know that there have wars fought over how the IF, THEN, DO and END should be indented and on which line the DO should appear...but I like to see a semi-colon at the end of each line and I like to have the ENDs line up with the IFs and the DO at the end of the THEN. But that's just me.

Without getting into the world of LOOPS, that's a somewhat artificial explanation of how IF statements work in SAS. You don't NEED to have a DO/END if you are only going to execute 1 statement, but you DO need to have a DO/END if you need to have 2 or more statements executed.

I now always follow the DO/END recommendation of my mentor, even if for 1 statement scenario....more often than not, I do go back and add more statements and thinking about the conditions and the DO/END, makes me clarify my logic. And for really, really complicated logic, I haul out my flowchart ruler and draw it out. Sometimes, the picture makes the coding easier.

my .02,

cynthia

Re: nested if-then/else grouping

CharlesR — Sat, 17 Jul 2010 23:41:01 GMT

Yep, you're right. I was trying to get all "fancy" by having the nested loops/do end statements, and i needed to break it down to my 8 permutations with 8 if/else if's. More straight forward this way.

Thanks!

Re: nested if-then/else grouping

CharlesR — Sat, 17 Jul 2010 23:41:31 GMT

hey thanks for all your help!!