SAS - PROC SORT identifying duplicate records

sas_proc_sort_duplicate_keys

/*This example demonstrates how to get a list of duplicates based on the key variables.
KEY variables are placed in the BY statement. 
Any 'duplicates' according to the KEY variables are kept in the OUT= dataset
*/

*Generate sample data with duplicate KEY;
data class;
    set sashelp.class sashelp.class(obs=5);
run;

*Use the NOUNIQUEKEYS to get rid of unique records and keep duplicates;
proc sort data=class nouniquekeys out=duplicates;
    by name;
run;