[英]get undefined value in mongodb MapReduce
我嘗試使用兩次MapReduce聚合來獲取每月唯一的用戶數。
第一個MR函數計算出mr_buyer_payment集合,如下所示:
{ "_id" : { "u" : "01329f19-27b0-435b-9ca1-450984024a31", "tid" : ISODate("2013-09-01T00:00:00Z") }, "value" : { "payment" : 38, "count_pay" : 1 } }
{ "_id" : { "u" : "264dd104-b934-490b-988e-5822fd7970f6", "tid" : ISODate("2013-09-01T00:00:00Z") }, "value" : { "payment" : 4.99, "count_pay" : 1 } }
{ "_id" : { "u" : "27bb8f72-a13e-4676-862c-02f41fea1bc0", "tid" : ISODate("2013-09-01T00:00:00Z") }, "value" : { "payment" : 11.98, "count_pay" : 2 } }
第二個MR函數適用於較小的數據集,但是當查詢增長到100條以上的記錄時,它將得到錯誤的結果,某些值為NaN。
調試日志在Reduce函數中顯示了一些值,例如v.payment,v.count_user變為未定義。
date:Sun Jun 30 2013 17:00:00 GMT-0700 (PDT) value:undefined / 162 / undefined
並連接了MR結果信息:
{
"result" : "mr_buyer_all",
"timeMillis" : 29,
"counts" : {
"input" : 167,
"emit" : 167,
"reduce" : 6, // it should be 3, as same as "output" number
"output" : 3
},
"ok" : 1,
}
這是第二MR功能:
db.mr_buyer_payment.mapReduce(
function(){
var key = this._id.tid;
var value = {
payment:this.value.payment,
count_pay:this.value.count_pay,
count_user:1
};
if (value.count_pay>0)
{
print("date:"+key+" u:"+this._id.u+"value:"+value.payment+" / "+value.count_pay+" / "+value.count_user);
emit(key,value);
}
},
function(key,values){
var result = {revenue:0,count_pay:0,user:0};
values.forEach(function(v){
if (!v.count_user)
{
print("date:"+key+" "+"value:"+v.payment+" / "+v.count_pay+" / "+v.count_user);
} else
{
result.revenue += v.payment;
result.count_pay += v.count_pay;
result.user += v.count_user;
}
});
return result;
},
{
out:{replace:"mr_buyer_all"}
}
)
Reduce函數中的子文檔應使用與Map函數中相同的格式。 所以解決方案是:
function(key,values){
// the following key must be as same as the object in map
var r = {payment:0,count_pay:0,count_user:0}
values.forEach(function(v){
r.payment += v.payment;
r.count_pay += v.count_pay;
r.count_user += v.count_user;
});
return r;
},
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