## BY Statement

**BY** * variables ***;**

You can specify a BY statement with PROC FASTCLUS to obtain separate
analyses on observations in groups defined by the BY variables.
When a BY statement appears, the procedure expects the input data set
to be sorted in order of the BY variables.
If your input data set is not sorted in ascending order,
use one of the following alternatives:

- Sort the data using the SORT procedure with a similar
BY statement.
- Specify the BY statement option NOTSORTED or DESCENDING
in the BY statement for the FASTCLUS procedure.
The NOTSORTED option does not mean that the data
are unsorted but rather that the data are arranged
in groups (according to values of the BY variables)
and that these groups are not necessarily in
alphabetical or increasing numeric order.
- Create an index on the BY variables using the DATASETS procedure.

If you specify the SEED= option and the SEED= data
set does not contain any of the BY variables, then
the entire SEED= data set is used to obtain initial
cluster seeds for each BY group in the DATA= data set.

If the SEED= data set contains some but not all of the BY
variables, or if some BY variables do not have the same type
or length in the SEED= data set as in the DATA= data set,
then PROC FASTCLUS displays an error message and stops.

If all the BY variables appear in the SEED= data set with the same
type and length as in the DATA= data set, then each BY group in the
SEED= data set is used to obtain initial cluster seeds for the
corresponding BY group in the DATA= data set. All BY groups in the
DATA= data set must also appear in the SEED= data set. The BY groups
in the SEED= data set must be in the same order as in the DATA= data
set. If you specify the NOTSORTED option
in the BY statement, there must be
exactly the same BY groups in the same order in both data sets. If
you do not specify NOTSORTED, some BY groups can appear in the SEED=
data set but not in the DATA= data set; such BY groups are not used in
the analysis.

For more information on the BY statement, refer to the discussion
in *SAS Language Reference: Concepts*.
For more information on the DATASETS procedure, refer to the
discussion in the *SAS Procedures Guide.*

Copyright © 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.