[{"key":1,"version":1,"status":"ACTIVE","date":"Jan/10"},{"key":1,"version":2,"date":"Feb/10","status":"DRAFT"},{"key":2,"version":1,"date":"March/10","status":"ACTIVE"},{"key":3,"version":1,"date":"April/10","status":"ACTIVE"},{"key":3,"version":2,"date":"May/10","status":"ACTIVE"},{"key":3,"version":3,"date":"Jun/10","status":"DRAFT"}]

db.collection.aggregate([{"$group":{"_id":"$key","version":{"$max":"$version"}}}])