The HPIMPUTE Procedure
ID variables ;
The optional ID statement lists one or more variables from the input data set that are transferred to the output data set. The ID statement accepts numeric and character variables. For example, when you specify the OUT= option in the PROC HPIMPUTE statement, the ID variables, followed by indicator variables and imputed variables, are added to the output data set.
By default, to avoid data duplication for large data sets, the HPIMPUTE procedure does not include any variables from the input data set in the output data sets. Therefore, the ID statement can be used to copy variables from the input data set to the output data set.
The variables in an ID statement must not appear in any INPUT statement; if they appear, an error is reported.