Working with Grouped or Sorted Observations

Review of SAS Tools

PROC SORT <DATA=SAS-data-set> <OUT=SAS-data-set> <NODUPRECS>;: sorts a SAS data set by the values of variables listed in the BY statement. If you specify the OUT= option, the sorted data are stored in a different SAS data set than the input data. The NODUPRECS option tells PROC SORT to eliminate identical observations.

BY <DESCENDING> variable-1 < . . . <DESCENDING> variable-n>;: in a DATA step causes SAS to create FIRST. and LAST. variables for each variable named in the statement. The value of FIRST.variable-1 is 1 for the first observation with a given BY value and 0 for other observations. Similarly, the value of LAST.variable-1 is 1 for the last observation for a given BY value and 0 for other observations. The BY statement can follow a SET, MERGE, MODIFY, or UPDATE statement in the DATA step; it cannot be used with an INPUT statement. By default, SAS assumes that data being read with a BY statement are in ascending order of the BY values. The DESCENDING option indicates that values of the variable that follow are in the opposite order, that is, largest to smallest.