Guava：通过反转Map构造一个Multimap [英] Guava: construct a Multimap by inverting a Map

问题描述

为什么Guava没有下面的工厂调用从正常的Map创建一个MultiMap？

why does Guava doesn't have the following factory call to create a MultiMap from a normal Map?

public static <K,V> MultiMap<K,V> invertMap(Map<V,K> map);

我有程序名称映射到调用它们的频率的整数。我想反转这个，所以我可以最终构造一个TreeMap，按调用计数排序，然后是导致一个或多个程序名称的键。

I have program-names mapped to an integer of how often they were called. I'd like to invert this, so that i can ultimately construct a TreeMap, sorted by call-count, which then are the keys leading to one or multiple program-names.

推荐答案

如何：

public static <K,V> Multimap<K,V> invertMap(Map<V,K> map) {
    return Multimaps.invertFrom(Multimaps.forMap(map), ArrayListMultimap.create());
}

似乎不需要专门的函数。您甚至可以很容易地回到 TreeMap ：

Doesn't seem like this requires a dedicated function. You can even get back to a TreeMap pretty easily:

Map<String, Integer> programCounts;
TreeMap<Integer, Collection<String>> map = 
    new TreeMap<>(
        Multimaps.invertFrom(
           Multimaps.forMap(programCounts),
           ArrayListMultimap.create()
        ).asMap()
    );

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