couchdb erlang reduce-聚合对象 [英] couchdb erlang reduce - aggregate object

问题描述

说我有一个发出以下对象的地图

Say I have a map that emits the following objects

{"basePoints": 2000, "bonusPoints": 1000}
{"basePoints": 1000, "bonusPoints": 50}
{"basePoints": 10000, "bonusPoints": 5000}

我如何在Erlang（不是javascript）中编写一个reduce方法，该方法将返回如下所示的聚合对象：

How could I write a reduce in Erlang (not javascript) that would return an aggregate object like this:

{"basePoints": 13000, "bonusPoints": 6050}

（如果我能帮助的话，我宁愿不必编写2个单独的视图来分别发出每个值）

(I would rather not have to write 2 separate views that emits each value separately if I can help it)

非常感谢！

推荐答案

您实际上不需要特殊的reduce，在这种情况下，您可以使用标准的 _sum ，因为它可以求和不仅是数字，还有数字数组。

You actually do not need special reduce, in this case you can use standard _sum, since it’s able to sum not only numbers, but also arrays of numbers.

只需发射 [basePointsNum，0] for basePoints 和 [0，bonusPointsNum] 的 bonusPoints 。或者，如果您在一个文档中同时拥有两个字段，则可能会发出 [basePointsNum，bonusPointsNum] 。

Just emit [basePointsNum, 0] for basePoints and [0, bonusPointsNum] for bonusPoints. Or if you have both fields in one doc you might emit [basePointsNum, bonusPointsNum].

-在 _sum 中，您将收到一个由两个数字组成的数组，每个数字都是相应索引列的总和。该功能似乎尚未公开，但是可同时用于CouchDB和PouchDB，并且运行迅速。

After reducing using built-in _sum you will receive an array of two numbers, each is a sum of appropriate index column. This feature seems to be undocumented, however works for both CouchDB and PouchDB, and it’s blazing fast.

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