MongoDB mapReduce案例分析二

    1、先看订单表orders的数据结构如下图

    这样的数据共有6条，如下，只列出了items这个字段

2、下面给出map函数

var mapFunction2 = function() {
for (var idx = 0; idx < this.items.length; idx++) {
var key = this.items[idx].sku;
var value = {
count: 1,
qty: this.items[idx].qty
};
emit(key, value);
}
};

3、写reduce函数

var reduceFunction2 = function(keySKU, countObjVals) {
reducedVal = { count: 0, qty: 0 };
for (var idx = 0; idx < countObjVals.length; idx++) {
reducedVal.count += countObjVals[idx].count;
reducedVal.qty += countObjVals[idx].qty;
}
return reducedVal;
};

4、写finalize函数

var finalizeFunction2 = function (key, reducedVal) {
reducedVal.avg = reducedVal.qty/reducedVal.count;
return reducedVal;
};

5、执行mapReduce函数

6、查看结果

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