SAS Certification Prep Guide, 4th Edition

Selecting Variables

Where to Specify DROP= and KEEP= Data Set Options

When match-merging, specify these options in either the DATA statement or the MERGE statement, depending on whether you want to reference the variables in that DATA step:

• To reference a variable in the original data set (in a subsetting IF statement, for example) specify the variable in the DROP= option in the DATA statement. Otherwise, you might get unexpected results and your variable would be uninitialized.

  data clinic.merged (drop=id);

• To not reference certain variables and exclude them from the new data set, specify them in the DROP= option in the MERGE statement.

  merge clinic.demog(in=indemog  
                    rename=(date=BirthDate))  
        clinic.visit(drop=weight in=invisit rename=(date=VisitDate)); ...