The HPREG Procedure
Many procedures in SAS software add the variables from the input data set when an observationwise output data set is created. The assumption of high-performance statistical procedures is that the input data sets can be large and contain many variables. For performance reasons, the output data set contains the following:
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those variables explicitly created by the statement
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variables listed in the ID statement
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distribution keys or hash keys that are transferred from the input data set
This enables you to add output data set information that is necessary for subsequent SQL joins without copying the entire input data set to the output data set. For more information about output data sets that are produced when PROC HPREG is run in distributed mode, see the section Output Data Sets in Chapter 3: Shared Concepts and Topics.