如何在数组中找到数组的最大值？

Question

mongodb数据库中的数据结构如下：

{
  "date": "20201005",
  "data":[
    [10, 20, 30, 40, 50],
    [60, 70, 80, 90, 10],
    [11, 12, 13, 14, 15]
  ]
}
{
  "date": "20201006",
  "data":[
    [12, 22, 32, 42, 52],
    [61, 77, 88, 98, 10],
    [11, 12, 13, 14, 15]
  ]
}
{
  "date": "20201007",
  "data":[
    [11, 21, 31, 41, 51],
    [16, 17, 18, 19, 10],
    [11, 12, 13, 14, 99]
  ]
}

并且你想在每个文档中找到数组内部数组的最大值，我想要得到的结果如下：

{"max": 99} // 99 can be find in document where "date"="20201007"

如何使用 $max 运算符做到这一点？

Answer 1

你可以使用

db.collection.aggregate([
  { //Restructure
    $unwind: "$data"
  },
  {
    $project: {
      "max": {//Max in each array
        "$max": "$data"
      }
    }
  },
  {
    $group: {
      "_id": null,
      "max": {//Max of whole data
        $max: "$max"
      }
    }
  }
])

play

如何在数组中找到数组的最大值？

How to find max value of an array inside array?

aggregation

mongodb

aggregation-framework