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 组操作中，是他们在完成期间确定总数的一种方式，例如确定组占集合总数的百分比.

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.

比如分组操作完成后，我知道A组的合计数量为50.他们是否可以将组的数量值作为总数的百分比来获取?

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?

或者我是否必须将结果保存到一个集合中，确定总数，然后返回并使用该组总数的计算百分比更新每个文档?

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，该字段设置 map、 可用的 Javascript 全局变量>reduce 和 finalize 函数.您可以向 scope 添加一个字段，并在 map 或 reduce 阶段跟踪总数，以最适合您的用例为准；然后您可以在 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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