mongoDB mapReduce：reduce函数返回普通对象而不是贴图

有没有可能使用reduce函数来返回平面对象而不是类似于贴图的对象

更多详情：

db.getCollection('calls').mapReduce(function () {
    emit(this.reportDate + '-' + this.reportTime, {
        from: this.caller,
        to: this.called,
        callEnds: this.callEnds,
        callBegins: this.callBegins,
        location: this.location
    });
}, function (k, v) {
    var result = {};
    v.forEach(function (value) {
        result.from = value.from;
        result.to = value.to;
        result.callBegins = value.callBegins;
        result.callEnds = value.callEnds;
        if (value.location) {
            result.location = value.location;
        }
    });
    return result;
}, {
   out: 'mapReducedCalls'
})

使用此选项，输出集合的文档都是

{ "_id" : "k",
  "value" : 
{ "from" : "b5c06aafa4be00db3d6acadb67b6ceef",
    "to" : "0afba72b041e3ccb5a62f0b0b44cceea",
    "callEnds" : "01/03/2013 10:45:44",
    "callBegins" : "01/03/2013 10:45:40",
    "location" : 44763
} 
}

而我更喜欢平面物体的形式，比如

{ "_id" : "k",
  "from" : "b5c06aafa4be00db3d6acadb67b6ceef",
  "to" : "0afba72b041e3ccb5a62f0b0b44cceea",
  "callEnds" : "01/03/2013 10:45:44",
  "callBegins" : "01/03/2013 10:45:40",
  "location" : 44763
}

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不，当前需要“value”字段（假设这就是您所说的类似于地图的东西）