Using the DROP= and KEEP= Data Set Options for Efficiency
The DROP= and KEEP= data set options are valid in both
the DATA statement and the SET statement. However, you can write a
more efficient DATA step if you understand the consequences of using
these options in the DATA statement rather than the SET statement.
In the DATA statement,
these options affect which variables SAS writes from the program data
vector to the resulting SAS data set. In the SET statement, these
options determine which variables SAS reads from the input SAS data
set. Therefore, they determine how the program data vector is built.
When you specify the DROP= or KEEP= option in the SET statement, SAS does not read the excluded variables into the program data vector. If ...
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