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使用MapReduce的我不想重新發布這個東西,但我感覺好像我已經輸入完全一樣的語法,因爲大多數的我擡頭問題的文件(行)的計數。我試圖簡單地計算出價格大於9000的行數。有人能告訴我我做錯了什麼嗎?獲得MongoDB中
var map1 = function(){
if(this.price > 9000) {
emit(this._id, {count: 1});
}
};
var red1 = function(keyId, values){
var count = 0;
values.forEach(function(v) {
count +=v['count'];
});
return{count: count};
}
db.plots.mapReduce(map1, red1, {out: "query1"})
我的結果落得這樣的...
> db.query1.find()
{ "_id" : ObjectId("5170609afa9e8646fc906815"), "value" : { "count" : 1 } }
{ "_id" : ObjectId("5170609afa9e8646fc906816"), "value" : { "count" : 1 } }
{ "_id" : ObjectId("5170609afa9e8646fc90681c"), "value" : { "count" : 1 } }
{ "_id" : ObjectId("5170609afa9e8646fc906834"), "value" : { "count" : 1 } }
{ "_id" : ObjectId("5170609afa9e8646fc90683e"), "value" : { "count" : 1 } }
{ "_id" : ObjectId("5170609afa9e8646fc906846"), "value" : { "count" : 1 } }
{ "_id" : ObjectId("5170609afa9e8646fc90684b"), "value" : { "count" : 1 } }
{ "_id" : ObjectId("5170609afa9e8646fc90684e"), "value" : { "count" : 1 } }
{ "_id" : ObjectId("5170609afa9e8646fc906851"), "value" : { "count" : 1 } }
{ "_id" : ObjectId("5170609afa9e8646fc90685a"), "value" : { "count" : 1 } }
{ "_id" : ObjectId("5170609afa9e8646fc906861"), "value" : { "count" : 1 } }
{ "_id" : ObjectId("5170609afa9e8646fc906864"), "value" : { "count" : 1 } }
{ "_id" : ObjectId("5170609afa9e8646fc906879"), "value" : { "count" : 1 } }
{ "_id" : ObjectId("5170609afa9e8646fc906882"), "value" : { "count" : 1 } }
{ "_id" : ObjectId("5170609afa9e8646fc906883"), "value" : { "count" : 1 } }
{ "_id" : ObjectId("5170609afa9e8646fc90688b"), "value" : { "count" : 1 } }
{ "_id" : ObjectId("5170609afa9e8646fc90688c"), "value" : { "count" : 1 } }
{ "_id" : ObjectId("5170609afa9e8646fc906891"), "value" : { "count" : 1 } }
{ "_id" : ObjectId("5170609afa9e8646fc906894"), "value" : { "count" : 1 } }
{ "_id" : ObjectId("5170609afa9e8646fc90689a"), "value" : { "count" : 1 } }
我想是剛剛得到一個單一的多少回。
太感謝你了!這清理了很多。是否發出(1,1);強制mapReduce使用我的整個集合作爲值?而且我假設你什麼時候分組_id:null它會「單獨」分組一切嗎? – 2013-04-20 03:38:30
基本上不管你發出1或null還是「foo」,它在地圖縮小或聚合中都沒有關係 - 它只是說按「常量」而不是字段的值對總和進行分組。 – 2013-04-20 03:51:58