You can specify a BY statement with PROC SIM2D to obtain separate analyses on observations in groups that are 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 you specify more than one BY statement, only the last one specified is used.

If your input data set is not sorted in ascending order, use one of the following alternatives:

• Sort the data by using the SORT procedure with a similar BY statement.

• Specify the NOTSORTED or DESCENDING option in the BY statement for the SIM2D 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 by using the DATASETS procedure (in Base SAS software).

In PROC SIM2D it makes sense to use the BY statement only in conditional simulations where observations are involved. In particular, using the BY statement assumes that you have specified an input data set with the DATA= option in the PROC SIM2D statement. In PROC SIM2D if you omit the VAR= option in the SIMULATE statement, then this is a request for unconditional simulation even if you have specified the DATA= option in the PROC SIM2D statement. Therefore, it is possible to specify the BY statement and request mixed types of simulations by specifying multiple SIMULATE statements in the same PROC SIM2D step.

A special case occurs when you omit the DATA= option in the PROC SIM2D statement, your unconditional simulation correlation model input comes from an item store in the RESTORE statement, and this store has its own BY groups. The SIM2D procedure exhibits then a BY-like behavior, even though you specified no BY statement. This behavior enables you to distinguish the simulation tasks that depend on models in the different store BY groups.

For more information about BY-group processing, see the discussion in SAS Language Reference: Concepts. For more information about the DATASETS procedure, see the discussion in the Base SAS Procedures Guide.