1

地図：

function () { 
emit(this.thread, 
    {max_year:this.date.getFullYear(), 
     min_year:this.date.getFullYear(), 
     max_month:this.date.getMonth(), 
     min_month:this.date.getMonth(),count:1});

};

Reduce:
function (key, values) {
max_year= values[0].max_year;
min_year = values[0].min_year;
max_month= values[0].max_month;
min_month = values[0].min_month;
var sum = 0;
if (values.length > 1){
    for(i in values){
        if(values[i].max_year > max_year){
            max_year = values[i].max_year;
        };
        if(values[i].min_year < min_year){
            min_year = values[i].min_year;
        };
        if(values[i].max_month > max_month){
            max_month = values[i].max_month;
        };
        if(values[i].min_month < min_month){
            min_month = values[i].min_month;
        };
        sum+=values[i].count
    };
};

return {"max year":max_year, "min year":min_year, "max month":max_month, "min month":min_month, "No of posts": sum};
}
};

出力：

{u'_id': u'Sujet  Top 5 TED POST', u'value': {u'No of posts': 8.0, u'min month': 0.0, u'max month': 6.0, u'max year': 2011.0, u'min year': 2010.0}}
{u'_id': u'Sujet  Top 5 des meilleurs guitaristes de lhistoire du Rock', u'value':       {u'No of posts': 42.0, u'min month': 2.0, u'max month': 10.0, u'max year': 2011.0, u'min year': 2009.0}}
{u'_id': u'Sujet  Top ALEJANDRO GONZALEZ INARRITU', u'value': {u'No of posts': 29.0, u'min month': 0.0, u'max month': 9.0, u'max year': 2011.0, u'min year': 2008.0}}
{u'_id': u'Sujet  Top ANDY et LARRY WACHOWSKY', u'value': {u'No of posts': 40.0, u'min month': 0.0, u'max month': 11.0, u'max year': 2011.0, u'min year': 2008.0}}
{u'_id': u'Sujet  Top BRYAN SINGER', u'value': {u'No of posts': 50.0, u'min month': 0.0, u'max month': 11.0, u'max year': 2011.0, u'min year': 2006.0}}
{u'_id': u'Sujet  Top Cinma 2010', u'value': {u'No of posts': nan, u'min month': None, u'max month': None, u'max year': None, u'min year': None}}
{u'_id': u'Sujet  Top Cinma 2011', u'value': {u'No of posts': nan, u'min month': None, u'max month': None, u'max year': None, u'min year': None}}

ご覧のとおり、一部のフィールド（「投稿数なし」）では「Nan」と出力され、他のフィールドでは非出力になります。これは、タイムスタンプを処理せずに投稿の数をカウントするためだけにMapReduceを実行した場合には発生しません。また、「投稿数」が多い場合（1000程度程度）にNanが印刷されていることにも気づきました。また、「カウント」と「合計」がない場合、最大年、最小年、月のすべての操作は適切です。ありがとうございました。

4

1 に答える 1

2

Your reduce function needs to return a value in the same format as the second argument to emit() -- because of the way MongoDB Map-Reduce works, the results of a reduce function may be passed in to reduce again. I suspect that this is where the nan and None are coming from. Specifically here, you just need to adjust the key names in the object you return from your reduce: for instance, rather than "max year" (in reduce) you should use max_year.

For more on writing correct map and reduce functions, see the MongoDB Map-Reduce documentation.

于 2012-04-13T15:04:12.533 に答える