You can specify a BY statement with PROC BOXPLOT to obtain separate box plots for each group defined by the levels of the BY variables. When you specify a BY statement, the input data set must 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 by using the SORT procedure with a similar BY statement.

• Specify the BY statement option NOTSORTED or DESCENDING in the BY statement for the BOXPLOT 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.

For more information about the BY statement, see SAS Language Reference: Concepts. For more information about the DATASETS procedure, see the Base SAS Procedures Guide.