在mongodb group/map命令中，确定组占总数的百分比 [英] In a mongodb group/map command determine the group's percentage of a total

问题描述

在mongodb分组操作中，它们是在完成期间确定总数的一种方法，以便eaxample确定在集合总数中的分组百分比.

In a mongodb group operation, is their a way to determine totals during finalization, for eaxample to determine the groups percentage of the collection's total.

例如，在完成分组操作后，我知道组A的总计数量为50. 他们是否可以获取组的数量值占总数的百分比?

For example, after the grouping operation is completed, I know that group A has an aggregate qty of 50. Is their a way to get the group's qty values as a percentage of the total?

还是我必须将结果保存到集合中，确定总数，然后返回并使用计算出的组总数百分比来更新每个文档?

Or do I have to save results to a collection, determine the totals, then go back and update each document with a calculated percentage of the total for the group?

推荐答案

MongoDB map-reduce支持scope字段，该字段将Javascript全局变量设置为可用于map，reduce和finalize函数.您可以在scope阶段添加一个字段，并在map或reduce阶段跟踪总数，以哪种情况最适合您的用例；您可以在finalize期间访问它，以计算每个输出组的百分比.

MongoDB map-reduce supports a scope field, which sets Javascript globals available to map, reduce, and finalize functions. You could add a field to scope and track the total during either map or reduce phases, whichever makes most sense for your use case; you can then access this during finalize to compute the percentage for each output group.

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