MongoDB: aggregation, $group by multiple (two) fields, with sorting (receiving latest) results

I want to receiving the following data

 item: 168652 groupedBy: { 1602 and 7 }, { 1603 and 5 }

1. You need to group at item at the last
2. Initially you need to group at realm, then you need to get latest timestamp i.e max

play

db.collection.aggregate([  {    $group: {      _id: {        connected_realm_id: "$connected_realm_id"      },      "data": {        "$max": "$last_modified"      },      "item": {        "$first": "$item.id"      }    }  },  {    $project: {      "connected_realm_id": "$_id.connected_realm_id",      "last_modified": "$data",      "item": 1,      "_id": 0    }  },  {    "$group": {      "_id": "$item",      "groupedBy": {        "$push": "$$ROOT"      }    }  }])

EDIT:

this one?

db.collection.aggregate([  {    $group: {      _id: {        connected_realm_id: "$connected_realm_id",        latest_timestamp: {          $max: "$last_modified"        },              },      data: {        $push: "$$ROOT"      }    }  },  {    "$unwind": "$data"  },  {    $group: {      _id: {        connected_realm_id: "$data.connected_realm_id"      },      "data": {        "$max": "$data.last_modified"      },      "item": {        "$first": "$data.item.id"      }    }  },  {    $project: {      "connected_realm_id": "$_id.connected_realm_id",      "last_modified": "$data",      "item": 1,      "_id": 0    }  },  {    "$group": {      "_id": "$item",      "groupedBy": {        "$push": "$$ROOT"      }    }  }])

Update:

As OP derived from above edit, this solves OP's problem

db.collection.aggregate([  {    $group: {      _id: {        connected_realm_id: "$connected_realm_id",        latest_timestamp: {          $max: "$last_modified"        },              },      data: {        $push: "$$ROOT"      }    }  },  {    "$unwind": "$data"  },  {    $group: {      _id: {        connected_realm_id: "$data.connected_realm_id"      },      "data": {        "$max": "$data.last_modified"      },      "item": {        "$push": "$data"      }    }  }])

The correct (final solution) at MongoPlayground

Dataset:

[  {    item: {      id: 168652    },    connected_realm_id: 1602,    last_modified: 1596719280  },  {    item: {      id: 168652    },    connected_realm_id: 1602,    last_modified: 1596719280  },  {    item: {      id: 168652    },    connected_realm_id: 1602,    last_modified: 1596719280  },  {    item: {      id: 168652    },    connected_realm_id: 1602,    last_modified: 1596719280  },  {    item: {      id: 168652    },    connected_realm_id: 1602,    last_modified: 2  },  {    item: {      id: 168652    },    connected_realm_id: 1602,    last_modified: 3  },  {    item: {      id: 168652    },    connected_realm_id: 1602,    last_modified: 4  },  {    item: {      id: 168652    },    connected_realm_id: 1602,    last_modified: 5  },  {    item: {      id: 168652    },    connected_realm_id: 1602,    last_modified: 1596719280  },  {    item: {      id: 168652    },    connected_realm_id: 1602,    last_modified: 1596719280  },  {    item: {      id: 168652    },    connected_realm_id: 1603,    last_modified: 1596719267  },  {    item: {      id: 168652    },    connected_realm_id: 1603,    last_modified: 1596719267  },  {    item: {      id: 168652    },    connected_realm_id: 1603,    last_modified: 1596719267  },  {    item: {      id: 168652    },    connected_realm_id: 1603,    last_modified: 1596719267  },  {    item: {      id: 168652    },    connected_realm_id: 1603,    last_modified: 1  },  {    item: {      id: 168652    },    connected_realm_id: 1603,    last_modified: 2  },  {    item: {      id: 168652    },    connected_realm_id: 1603,    last_modified: 3  },  {    item: {      id: 168652    },    connected_realm_id: 1603,    last_modified: 4  },  {    item: {      id: 168652    },    connected_realm_id: 1603,    last_modified: 5  },  {    item: {      id: 168652    },    connected_realm_id: 1603,    last_modified: 1596719267  }]

Aggregation Query

db.collection.aggregate([  {    $group: {      _id: {        connected_realm_id: "$connected_realm_id"      },      latest: {        $max: "$last_modified"      },      data: {        $push: "$$ROOT"      }    }  },  {    $unwind: "$data"  },  {    $addFields: {      "data.latest": {        $cond: {          if: {            $eq: [              "$data.last_modified",              "$latest"            ]          },          then: "$latest",          else: "$false"        }      }    }  },  {    "$replaceRoot": {      "newRoot": "$data"    }  },  {    "$match": {      "latest": {        "$exists": true,        "$ne": null      }    }  }])