[{"_id":{"$oid":"5bef93fc1c4b3236e79f9c25"},"Created_at":"Sat Nov 17 04:07:12 +0000 2018","ID":{"$numberLong":"1063644700727480320"},"Category":"A"},{"_id":{"$oid":"5bef93531c4b3236e79f9c11"},"Created_at":"Sat Nov 17 05:17:12 +0000 2018","ID":{"$numberLong":"1063644018276360192"},"Category":"B"},{"_id":{"$oid":"5bef94e81c4b3236e79f9c3b"},"Created_at":"Sat Nov 17 05:17:12 +0000 2018","ID":{"$numberLong":"1063644018276360192"},"Category":"B"},{"_id":{"$oid":"5bef94591c4b3236e79f9cee"},"Created_at":"Sat Nov 17 05:17:12 +0000 2018","ID":{"$numberLong":"1063644700727481111"},"Category":"C"}]

db.collection.aggregate([{"$group":{"_id":"$ID","uniqueCategories":{"$addToSet":"$Category"},"uniqueIds":{"$addToSet":"$_id"},"count":{"$sum":1}}}])