Sum of Distinct/Unique values in Header for ETEXT template

Summary: Sum of Distinct/Unique values in Header for ETEXT template

Content (required): I have 4 records for same person in my xml. All 4 records have same salary($2000) value. In my detail record I have done grouping and im able to display unique single row for the person, but in header record when i try sum(salary) its giving me $8000. But my expectation is to display $2000. I want to sum unique values in header.

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