反向分类减速键 [英] Reverse Sorting Reducer Keys

问题描述

将地图输出键以相反顺序放到缩小器的最佳方法是什么？默认情况下，减速器以按键的升序接收所有的键。任何帮助或意见广泛赞赏。简单的说，在正常情况下，如果一张地图发出键 1,4,3,5,2 ，缩减器会收到相同的作为 1,2,3,4,5 。我想减速机接受 5,4,3,2,1 。

解决方案

在Hadoop 1.X中，您可以使用 JobConf.setOutputKeyComparatorClass 。

您的比较器必须实现 RawComparator 界面。

使用Hadoop 2.X，可以使用 Job.setSortComparatorClass ，执行 RawComparator 。

What is the best approach to get the Map Output keys to a reducer in reverse order? By default the reducer receives all keys in ascending order of keys. Any help or comments widely appreciated.

In simple words, in the normal scenario, if a map emits keys 1,4,3,5,2 the reducer receives the same as 1,2,3,4,5. I would like the reducer to receive 5,4,3,2,1 instead.

解决方案

In Hadoop 1.X, you can specify a custom comparator class for your outputs using JobConf.setOutputKeyComparatorClass.

Your comparator must implement the RawComparator interface.

With Hadoop 2.X, this is done by using Job.setSortComparatorClass, still with an implementation of RawComparator.

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