08-21-2014 10:11 AM
this week I was updating an old sas program.
Several times the developer was MERGING several data sets AND at the same time using xxx.FIRST and yyy.LAST statements.
I never do these things together. I think unexpected results can come up?
08-21-2014 11:10 AM
This is just a stage you're going through. The more you learn about how MERGE works, the less you will see unexpected results. Eventually, you will know enough about it so that you can anticipate and code around any of the problems.
Typically the case you describe involves the use of a subsetting IF in combination with a BY statement. A subsetting IF can delete an observation having FIRST.xxx or LAST.yyy equal to 1. That is likely to give you an undesirable result.
Good luck and don't stop learning.
08-21-2014 11:13 AM
As far as I can remember you can have some issues using a by when values get retained when you wouldn't expect them to. This can cause problems when an IF statement doesn't give you the value you expect. It does make sense when you think in terms of how the PDV works but it is counter-intuitive and easily catches people out.
08-22-2014 12:32 PM
Can you please provide me with a best example to use first. and last....I've just started learning SAS and want to make my concept clear on first. and last. statement.