Specifies columns (variables) to be saved to the output dataset in a data loop.
keep age, pay, sex;
Commas are optional in variable_list.
Retains only the specified variables in the output dataset. Any
variables referenced must already exist, either as elements of the
source dataset, or as the result of a previous
vector, or code
drop is used, the output dataset will contain all
variables from the source dataset, as well as any newly defined
variables. The effects of multiple
drop statements are