mongo-mapreduce測試（1）——count/sum/where條件

mongo-mapreduce測試（2）——列轉(zhuǎn)行與finalize函數(shù)

mongo-mapreduce測試（3）——group by having

mongo-mapreduce測試（4）——avg

mongo-mapreduce測試（5）——max/min

mongo-mapreduce測試（6）——綜合測試

mongo-mapreduce測試（7）——使用js存儲過程

mongo-mapreduce測試（8）——階段總結(jié)（1）

mongo-mapreduce測試（9）——python調(diào)用

mongo-mapreduce測試（10）——階段總結(jié)（2）

mongo-mapreduce測試（11）——跟蹤調(diào)試

測試mapreduce的avg聚合函數(shù)的實現(xiàn)，類似如下SQL：

select name, avg(dic)
from tianyc_test3
group by name;

1. 測試數(shù)據(jù)如下：

> db.tianyc_test3.find()
{ "_id" : ObjectId("51258e47ff13bc6383473137"), "name" : "xtt", "dic" : 1 }
{ "_id" : ObjectId("51258e49ff13bc6383473138"), "name" : "xtt", "dic" : 2 }
{ "_id" : ObjectId("51258e4bff13bc6383473139"), "name" : "xtt", "dic" : 3 }
{ "_id" : ObjectId("51258e4eff13bc638347313a"), "name" : "xtt", "dic" : 4 }
{ "_id" : ObjectId("51258e50ff13bc638347313b"), "name" : "xtt", "dic" : 5 }
{ "_id" : ObjectId("51258e5aff13bc638347313c"), "name" : "yct", "dic" : 1 }
{ "_id" : ObjectId("51258e5cff13bc638347313d"), "name" : "yct", "dic" : 2 }
{ "_id" : ObjectId("51258e62ff13bc638347313e"), "name" : "neu", "dic" : 1 }
{ "_id" : ObjectId("51258e64ff13bc638347313f"), "name" : "neu", "dic" : 2 }
{ "_id" : ObjectId("51258e65ff13bc6383473140"), "name" : "neu", "dic" : 3 }
{ "_id" : ObjectId("51258e68ff13bc6383473141"), "name" : "neu", "dic" : 4 }

2. 編寫map函數(shù)

> var m = function(){
... emit(this.name,{dic:this.dic});
... }

3. 編寫reduce函數(shù)

> var r = function (key,values) {
... var sum = 0;
... for (var i=0; i<values.length; i++) {
... sum += values[i].dic;
... }
... return {name:key, avg: sum/values.length};
... };

4. 執(zhí)行mapreduce
> var res = db.runCommand({
... mapreduce:'tianyc_test3',
... map:m,
... reduce:r,
... out:'tianyc_mr_Result1'
... }
... )

5. 查詢結(jié)果

> db.tianyc_mr_Result1.find()
{ "_id" : "neu", "value" : { "name" : "neu", "avg" : 2.5 } }
{ "_id" : "xtt", "value" : { "name" : "xtt", "avg" : 3 } }
{ "_id" : "yct", "value" : { "name" : "yct", "avg" : 1.5 } }
>

總結(jié)

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