If you want to use a task in Eguide, then the Sort Data task can be used, but you may have to use the task twice. The first time you would sort by all 3 variables, but make sure the sort order for Registration_Date is set to 'Descending', so the most recent date is the first observation for each Person and Registration group.
Then in the 2nd Sort Data task (used on the previously sorted output data set from the 1st Sort Data task), you would only sort by Person and Registration, and in the Options section under 'Duplicate Records', select "Keep only the first record for each 'Sort by' group" This will remove any duplicate observations for Person and Registration.
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