如何创建Multimap< K，V>来自地图< K，Collection< V>>？ [英] How to create a Multimap<K,V> from a Map<K, Collection<V>>?

问题描述

我没有找到这样的多图构造...当我想要这样做时，我遍历地图，并填充多图。还有其他方法吗？

I didn't find such a multimap construction... When I want to do this, I iterate over the map, and populate the multimap. Is there an other way?

final Map<String, Collection<String>> map = ImmutableMap.<String, Collection<String>>of(
            "1", Arrays.asList("a", "b", "c", "c"));
System.out.println(Multimaps.forMap(map));

final Multimap<String, String> expected = ArrayListMultimap.create();
for (Map.Entry<String, Collection<String>> entry : map.entrySet()) {
    expected.putAll(entry.getKey(), entry.getValue());
}
System.out.println(expected);

第一个结果是 {1 = [[a，b，c， c]]} 但我希望 {1 = [a，b，c，c]}

The first result is {1=[[a, b, c, c]]} but I expect {1=[a, b, c, c]}

推荐答案

假设你有

Map<String, Collection<String>> map = ...;
Multimap<String, String> multimap = ArrayListMultimap.create();

然后我相信这是你能做的最好的

Then I believe this is the best you can do

for (String key : map.keySet()) {
  multimap.putAll(key, map.get(key));
}

或更优，但更难阅读

for (Entry<String, Collection<String>> entry : map.entrySet()) {
  multimap.putAll(entry.getKey(), entry.getValue());
}

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