Mongodb是否可以聚合对象?

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我正在尝试汇总此文档中的数据包总数.

I am trying to aggregate the total sum of packets in this document.

{ "_id" : ObjectId("51a6cd102769c63e65061bda"), "capture" : "1369885967", "packets" : { "0" : "595", "1" : "596", "2" : "595", "3" : "595", ... } }

我能找到的最接近的是

db.collection.aggregate({ $match: { capture : "1369885967" } }, {$group: { _id:null, sum: {$sum:"$packets"}}});

但是它返回总和0，这显然是错误的.

However it returns sum 0, which is obviously wrong.

{ "result" : [ { "_id" : null, "sum" : 0 } ], "ok" : 1 }

如何获取所有数据包的总和?

How do I get the sum of all the packets?

推荐答案

由于您将值保存在对象而不是数组中，因此需要使用mapReduce.

Since you have the values in an object instead of an array, you'll need to use mapReduce.

// Emit the values as integers var mapFunction = function() { for (key in this.packets) { emit(null, parseInt(this.packets[key])); } } // Reduce to a simple sum var reduceFunction = function(key, values) { return Array.sum(values); } > db.collection.mapReduce(mapFunction, reduceFunction, {out: {inline:1}}) { "results" : [ { "_id" : null, "value" : 2381 } ], "ok" : 1, }

如果可能的话，应该将值作为数字类型的数组发出，因为这会给您更多选择(即聚合)，并且(除非数据集很大)可能会带来性能上的好处.

If at all possible, you should emit the values as an array of a numeric type instead since that gives you more options (ie aggregation) and (unless the data set is large) probably performance benefits.