Selecting the earliest hit for a specific field

Lets say I have 1000 Documents in an index each containing a field name and a field reportDate. I know I can aggregate against these fields to find the amount of Documents per unique name and I know I can sort them by date entered. What I can't figure out is how to get only the earliest entered document per unique name.

For Example; Lets say we had the following documents:

  1. { name: Sam, reportDate: 2016-03-17 }

  2. { name: Sam, reportDate: 2016-03-13 }

  3. { name: Joe, reportDate: 2016-04-03 }

  4. { name: Joe, reportDate: 2016-05-19 }

After the query I would want only Documents 2 and 3 to be hits; The earliest report per name.