The COMPARE Procedure

BY Statement

Produces a separate comparison for each BY group.

Main discussion: BY

BY <DESCENDING> variable-1
<...<DESCENDING> variable-n>
<NOTSORTED>;

Required Arguments

variable: specifies the variable that the procedure uses to form BY groups. You can specify more than one variable. If you do not use the NOTSORTED option in the BY statement, the observations in the data set must be sorted by all the variables that you specify. Variables in a BY statement are called BY variables.

Options

DESCENDING: specifies that the observations are sorted in descending order by the variable that immediately follows the word DESCENDING in the BY statement.
NOTSORTED: specifies that observations are not necessarily sorted in alphabetic or numeric order. The observations are grouped in another way, for example, chronological order.

The requirement for ordering observations according to the values of BY variables is suspended for BY-group processing when you use the NOTSORTED option. The procedure defines a BY group as a set of contiguous observations that have the same values for all BY variables. If observations with the same values for the BY variables are not contiguous, the procedure treats each contiguous set as a separate BY group.

BY Processing with PROC COMPARE
To use a BY statement with PROC COMPARE, you must sort both the base and comparison data sets by the BY variables. The nature of the comparison depends on whether all BY variables are in the comparison data set and, if they are, whether their attributes match those of the BY variables in the base data set. The following table shows how PROC COMPARE behaves under different circumstances:

Condition Behavior of PROC COMPARE

All BY variables are in the comparison data set and all attributes match exactly Compares corresponding BY groups

None of the BY variables are in the comparison data set Compares each BY group in the base data set with the entire comparison data set

Some BY variables are not in the comparison data set Writes an error message to the SAS log and terminates

Some BY variables have different types in the two data sets Writes an error message to the SAS log and terminates

Condition	Behavior of PROC COMPARE
All BY variables are in the comparison data set and all attributes match exactly	Compares corresponding BY groups
None of the BY variables are in the comparison data set	Compares each BY group in the base data set with the entire comparison data set
Some BY variables are not in the comparison data set	Writes an error message to the SAS log and terminates
Some BY variables have different types in the two data sets	Writes an error message to the SAS log and terminates

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