如何在mongodb中使用聚合？

好吧，我有一个总共约30000个拉链。

它们看起来像这样...

{ "city" : "EPES", "loc" : [ -88.161443, 32.763371 ], "pop" : 1391, "state" : "AL", "_id" : "35460" } 
{ "city" : "ETHELSVILLE", "loc" : [ -88.221987, 33.386816 ], "pop" : 719, "state" : "AL", "_id" : "35461" } 
{ "city" : "EUTAW", "loc" : [ -87.930297, 32.888871 ], "pop" : 6586, "state" : "AL", "_id" : "35462" } 
{ "city" : "FOSTERS", "loc" : [ -87.735688, 33.135859 ], "pop" : 2100, "state" : "AL", "_id" : "35463" } 
{ "city" : "GAINESVILLE", "loc" : [ -88.271558, 32.908364 ], "pop" : 1051, "state" : "AL", "_id" : "35464" } 
{ "city" : "GORDO", "loc" : [ -87.900504, 33.346917 ], "pop" : 4333, "state" : "AL", "_id" : "35466" } 
{ "city" : "KNOXVILLE", "loc" : [ -87.791855, 32.982423 ], "pop" : 373, "state" : "AL", "_id" : "35469" } 
{ "city" : "COATOPA", "loc" : [ -88.173592, 32.588509 ], "pop" : 6055, "state" : "AL", "_id" : "35470" } 
{ "city" : "CYPRESS", "loc" : [ -87.615134, 32.978853 ], "pop" : 2659, "state" : "AL", "_id" : "35474" } 
{ "city" : "NORTHPORT", "loc" : [ -87.591441, 33.283425 ], "pop" : 20114, "state" : "AL", "_id" : "35476" }

我需要4最邮政编码找到利用它聚集的状态......我不知道。

任何帮助理解

来源

2012-11-15 thefonso

我假设这是作业吗？从一个“聚合”电话开始，每个州都会产生一些邮政编码，然后从那里开始。 – JohnnyHK

正如我所说...不知道。我正在看mongo网站上的例子，以获得线索...... http://docs.mongodb.org/manual/tutorial/aggregation-examples/ – thefonso

溶液：

db.zips.aggregate([ {$group:{_id:{state:"$state"},numberOfzipcodes:{$sum:1}}}, {$sort:{numberOfzipcodes:-1}}, {$limit:4}])

来源

2012-11-15 21:33:50 thefonso

//组通过状态，然后找到总的邮政编码中的每个状态，排序总数的邮政编码//降序订购。然后使用跳过跳过前3个状态并限制为1

db.zips.aggregate（[{$ group：{_ id：{state：“$ state”}，zips：{$ sum：1}}} ，{$ sort：{zips：-1}}，{$ skip：3}，{$ limit：1}]）

来源

2013-05-16 07:46:58

如何在mongodb中使用聚合？

回答

相关问题