When only a subset of a data file is needed, it is inefficient to extract all the data and then subset it in a subsequent DATA step. Instead, you can use the DATASOURCE procedure options and statements to extract only needed information from the data file.
The DATASOURCE procedure offers the following subsetting capabilities:
the INTERVAL= option controls the frequency of data output
the KEEP or DROP statement selects a subset of time series variables
the RANGE statement restricts the time range of data
the WHERE statement selects a subset of cross sections