Input/Output

[talzy7]

Okay that makes sense. So I am assuming the following statement causes Start_Date to change to 01JUL2017:

if Start_Date = '01DEC2016'd then do;
Start_Date = '01JUL2017'd;
End_Date = '31JUL2017'd;
output;
end;

What method can be used so that 01DEC2016 is recognized as Winter and 01JUL2017 as summer without compromising the above statement? Thank you for all your help by the way.

[Astounding]

The smallest changes to the program would involve consolidating the calculations. 

I'm making some assumptions on where I think you are headed.  For example, I think you want all the observations, not just those that satisfy the WHERE statement.  And I think you want 01DEC2016 output only once.  My best guess:

data work.extended;
set prg.discount2016;
if Start_Date = '01DEC2016'd then do;
   Promotion = 'Holiday Bonus';

   Season = 'Winter';
   output;

   Promotion = ' ';

   Season = ' ';

   Start_Date = '01JUL2017'd;

   End_Date = '31JUL2017'd;

   output;
end;

else if start_date = '01DEC2016'd then do;

   season = 'Summer';

   output;

end;

else output;
drop Unit_Sales_Price;
run;

[talzy7]

Thanks. I included the where statement because I am only wanting to output the 01DEC2016 and 01JUL2017 observations. When I use the method described above only winter is shown not summer.

[Astounding]

OK, I know I was guessing a little at the desired results.  It's clear now (I think).  Here's a rewrite:

data work.extended;
set prg.discount2016;

where Start_Date = '01DEC2016'd;
   Promotion = 'Holiday Bonus';

   Season = 'Winter';
   output;

   Promotion = ' ';

   Start_Date = '01JUL2017'd;

   End_Date = '31JUL2017'd;

   season = 'Summer';

   output;
drop Unit_Sales_Price;
run;

[talzy7]

Thank you soooo much for your help. I have learnt a lot!!