{ device: "M57906", date: some date }

h4s> db.events.aggregate([\{ $sort: { device: 1, date: 1 } }, \{ $group: { _id: "$device", obj: { $bottom: { output: "$date", sortBy: { date: -1 } } } } }])
[ \{ _id: 'M57906', obj: ISODate('2025-08-28T09:46:33.017Z') } ]
h4s> db.events.aggregate([\{ $sort: { device: 1, date: 1 } }, \{ $group: { _id: "$device", obj: { $bottomN: { n: 1, output: "$date", sortBy: { date: -1 } } } } }])
[ \{ _id: 'M57906', obj: [ ISODate('2025-07-06T00:00:01.305Z') ] } ]

            isCached: false,
            stage: 'PROJECTION_COVERED',
            transformBy: \{ date: 1, device: 1, _id: 0 },
            inputStage: {
              stage: 'DISTINCT_SCAN',
              keyPattern: \{ device: 1, date: 1 },
              indexName: 'device_1_date_1',
              isMultiKey: false,
              multiKeyPaths: \{ device: [], date: [] },
              isUnique: false,
              isSparse: false,
              isPartial: false,
              indexVersion: 2,
              direction: 'backward',
              indexBounds: {
                device: [ '[MaxKey, MinKey]' ],
                date: [ '[MaxKey, MinKey]' ]
              }
            }

{
  isCached: false,
  queryPlan: {
    stage: 'GROUP',
    planNodeId: 3,
    inputStage: {
      stage: 'PROJECTION_COVERED',
      planNodeId: 2,
      transformBy: \{ date: true, device: true, _id: false },
      inputStage: {
        stage: 'IXSCAN',
        planNodeId: 1,
        keyPattern: \{ device: 1, date: 1 },
        indexName: 'device_1_date_1',
        isMultiKey: false,
        multiKeyPaths: \{ device: [], date: [] },
        isUnique: false,
        isSparse: false,
        isPartial: false,
        indexVersion: 2,
        direction: 'forward',
        indexBounds: {
          device: [ '[MinKey, MaxKey]' ],
          date: [ '[MinKey, MaxKey]' ]
        }
      }
    }
  },
  slotBasedPlan: {
    slots: '$$RESULT=s9 env: \{ s4 = SortSpec({"date" : -1}) }',
    stages: '[3] project [s9 = newBsonObj("_id", s6, "obj", s8)] \n' +
      '[3] project [s8 = aggBottomNFinalize(s7, s4)] \n' +
      '[3] group [s6] [s7 = aggBottomN(s4, null, getSortKeyDesc(s2), (s2 ?: null)) init\{[[], 0ll, 1ll, 0, 104857600, true]}] spillSlots[s5] mergingExprs[aggBottomNMerge(s5, s4)] \n' +
      '[3] project [s6 = (s1 ?: null)] \n' +
      '[1] ixseek KS(0A0A0104) KS(F0F0FE04) none s3 none none lowPriority [s1 = 0, s2 = 1] @"edc48567-cea3-4782-97fe-7173105114f2" @"device_1_date_1" true '
  }
}