Question

我在MongoDB中有一个如下所示的数据集：

{ "name": "Tom's", "category": "coffee shop" },
{ "name": "Red Lobster", "category": "restaurant" },
{ "name": "Tom's", "category": "coffee shop" },
{ "name": "Starbucks", "category": "coffee shop" },
{ "name": "Central Park", "category": "park" },
{ "name": "Office", "category": "office" },
{ "name": "Red Lobster", "category": "restaurant" },
{ "name": "Home", "category": "home" },
{ ... } // and so on

如何找到特定类别的最常见值？例如，coffee shop和restaurant最常见的值应分别为Tom's和Red Lobster

我当前的$aggregate查询似乎只列出了所有数据集中最常见的值：

db.collection.aggregate(
{ "$group": { "_id": { "name": "$name" }, "count": { "$sum":1 } }}, 
{ "$group": { "_id": "$_id.name", "count": { "$sum": "$count" } }}, 
{ "$sort": { "count":-1 }}
)

Answer 1

您可以尝试以下查询。

$group关于类别和名称，以获取每个类别和名称组合的计数。

$sort输入文件按类别和计数desc。

$group在$first类别中选择最常出现的文档。

db.collection_name.aggregate([
  {
    "$group": {
      "_id": {
        "category": "$category",
        "name": "$name"
      },
      "count": {
        "$sum": 1
      }
    }
  },
  {
    "$sort": {
      "_id.category": 1,
      "count": -1
    }
  },
  {
    "$group": {
      "_id": {
        "category": "$_id.category"
      },
      "name": {
        "$first": "$_id.name"
      },
      "count": {
        "$first": "$count"
      }
    }
  }
])

如何在MongoDB中找到特定类别的最常见值？

1 个答案: