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如何使用$ avg来平均数组内的字段

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我正在使用Mongodb 3.2，我需要计算数组内的所有字段

这些是我收藏的一个例子

{
  "memTotal" : 33730525659,
  "swapTotal" : 16936129790,
  "queueList" : [
    {
      "usedSlots" : 2,
      "totalSlots" : 8,
      "reservedSlots" : 0,
    },
    {
      "usedSlots" : 2,
      "totalSlots" : 8,
      "reservedSlots" : 0,
    },
    {
      "usedSlots" : 2,
      "totalSlots" : 8,
      "reservedSlots" : 0,
    },
  ],
},
{
  "memTotal" : 33730525659,
  "swapTotal" : 16936129790,
  "queueList" : [
    {
      "usedSlots" : 2,
      "totalSlots" : 8,
      "reservedSlots" : 0,
    },
    {
      "usedSlots" : 2,
      "totalSlots" : 8,
      "reservedSlots" : 0,
    },
    {
      "usedSlots" : 2,
      "totalSlots" : 8,
      "reservedSlots" : 0,
    },
  ],
},
{
  "memTotal" : 33730525659,
  "swapTotal" : 16936129790,
  "queueList" : [
    {
      "usedSlots" : 2,
      "totalSlots" : 8,
      "reservedSlots" : 0,
    },
    {
      "usedSlots" : 2,
      "totalSlots" : 8,
      "reservedSlots" : 0,
    },
    {
      "usedSlots" : 2,
      "totalSlots" : 8,
      "reservedSlots" : 0,
    },
  ],
},

我需要计算“queueList.useSlots”，“queueList.totalSlots”，“queueList.totalSlots”的平均值，请记住queueList是一个数组 .

到目前为止，我所做的是使用聚合，首先是我{$ unwind：“queueList”}，{$ group：{useSlots：{$ avg：“queueList.useSlots”}}}

但这会返回错误的平均值:-(

任何帮助将非常感激:-)谢谢！

mongodb aggregation-framework

1 回答

  • 2

    请尝试以下查询 .

    db.memory.aggregate([
{$unwind : "$queueList"}, 
{$group : {_id : "$_id",
   "avgUseSlots" :{$avg :  "$queueList.usedSlots"},
   "avgTotSlots" :{$avg :  "$queueList.totalSlots"},
   "avgReservedSlots" :{$avg :  "$queueList.reservedSlots"}
   }
   }
 ]);

    Output:-

    {
    "_id" : ObjectId("57816e7285ae6441865d83e4"),
    "avgUseSlots" : 2,
    "avgTotSlots" : 8,
    "avgReservedSlots" : 0
}
    回复于

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