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MERGE and using .FIRST and/or .LAST notation

Frequent Contributor
Posts: 89

MERGE and using .FIRST and/or .LAST notation

Hi all,

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?




Super User
Posts: 6,759

Re: MERGE and using .FIRST and/or .LAST notation


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 or LAST.yyy equal to 1.  That is likely to give you an undesirable result.

Good luck and don't stop learning.

New Contributor
Posts: 2

Re: MERGE and using .FIRST and/or .LAST notation

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.

Not applicable
Posts: 1

Re: MERGE and using .FIRST and/or .LAST notation

Hi Jeheuk,

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.



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