Question

我使用的是Mongodb 3.2，我需要计算数组中的所有字段

这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＆＃34; queueList.useSlots＆＃34;，＆＃34; queueList.totalSlots＆＃34;，＆＃34; queueList.totalSlots＆＃34;的平均值，请记住queueList是一个阵列。

到目前为止，我所做的是使用聚合，首先是我{$ unwind：＆＃34; queueList＆＃34;}，{$ group：{useSlots：{$ avg：＆＃34; queueList.useSlots＆＃34; }}

但这会返回错误的平均值： - （

任何帮助将非常感谢:-)谢谢！

Answer 1

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"}
   }
   }
 ]);

<强>输出： -

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

如何使用$ avg来平均数组内的字段

1 个答案: