if & where statements

[librasonali]

Hello, 
I have a doubt in the number of observations .

question : create a temporary data set, cleandata36.
In this data set, convert all group values to upper case.
Then keep only observations with group equal to 'A' or 'B'.

when I run  below code 

data cleandata36;
set cert.input36 ;
if upcase(group) in ('A','B');
run;

then number of observations are different 

but when I run 

data cleandata36;
set cert.input36 ;
group=upcase(group);

where group in ('A','B');
run;

the number of observations are different. 

but the logic I want to implement is maybe same. Can please anyone tell me that why there is mismatch of observations 🙂 

[Kurt_Bremser]

The WHERE statement is applied to the input dataset, and therefore to the raw values. To make it work, use the function in the statement:

where upcase(group) in ('A','B');

[PeterClemmensen · Accepted solution]

The Where Statement is a compile-time statement. It controls what observations are being read into the data step. Meaning that in the code below, it considers the values read - NOT the upcased values. 

The Subsetting If Statement is considered at run-time. Therefore, in the code below, it considers the upcased values.

Hope this makes sense 🙂

data have;
input group :$1;
datalines;
A
a
B
b
; 

data test1;
   set have;
   group = upcase(group);
   where group in ('A', 'B');
run;

data test2;
   set have;
   group = upcase(group);
   if group in ('A', 'B');
run;

[librasonali]

so basically , whatever i will write above where ?? it won't take that condition in observation ?

[Kurt_Bremser]

The position of a WHERE statement in the code is irrelevant, as it is applied in the read engine for the incoming dataset. A WHERE statement has the same function that a WHERE= dataset option has, and in a certain sense you can consider it to work "outside" the data step.

I also recommend that you study the documentation of the WHERE Statement thoroughly.