如何创建一个多地图从地图>?

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?

我没有找到这么多地图的构造…当我想这样做时，我遍历映射，并填充multimap。还有别的办法吗?

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);

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

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

5 个解决方案

#1

Assuming you have

假设您已经

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

Then I believe this is the best you can do

我相信这是你能做到的最好的。

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

or the more optimal, but harder to read

或者更优，但更难以阅读。

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

#2

Here is a useful generic version that I wrote for my StuffGuavaIsMissing class.

这里有一个有用的通用版本，我为我的StuffGuavaIsMissing类编写了这个版本。

/**
 * Creates a Guava multimap using the input map.
 */
public static <K, V> Multimap<K, V> createMultiMap(Map<K, ? extends Iterable<V>> input) {
  Multimap<K, V> multimap = ArrayListMultimap.create();
  for (Map.Entry<K, ? extends Iterable<V>> entry : input.entrySet()) {
    multimap.putAll(entry.getKey(), entry.getValue());
  }
  return multimap;
}

And an immutable version:

和一个不可变的版本:

/**
 * Creates an Immutable Guava multimap using the input map.
 */
public static <K, V> ImmutableMultimap<K, V> createImmutableMultiMap(Map<K, ? extends Iterable<V>> input) {
  ImmutableMultimap.Builder<K, V> builder = ImmutableMultimap.builder();
  for (Map.Entry<K, ? extends Iterable<V>> entry : input.entrySet()) {
    builder.putAll(entry.getKey(), entry.getValue());
  }
  return builder.build();
}

#3

This question is a little old, but I thought I'd give an updated answer. With Java 8 you could do something along the lines of

这个问题有点老了，但我想我会给出一个更新的答案。用Java 8，你可以做一些事情。

ListMultimap<String, String> multimap = ArrayListMultimap.create();
Map<String, Collection<String>> map = ImmutableMap.of(
                           "1", Arrays.asList("a", "b", "c", "c"));
map.forEach(multimap::putAll);
System.out.println(multimap);

This should give you {1=[a, b, c, c]}, as desired.

这将根据需要给您{1=[a, b, c, c]}。

#4

UPDATE: For what you're asking, I think you're going to need to fall back to Multimap.putAll.

更新:对于你所问的问题，我认为你需要回到Multimap.putAll。

#5

Following code without Google's Guava library. It is used for double value as key and sorted order

以下代码没有谷歌的Guava库。它被用于作为键和排序顺序的双值。

Map<Double,List<Object>> multiMap = new TreeMap<Double,List<Object>>();

for( int i= 0;i<15;i++)
{
    List<Object> myClassList = multiMap.get((double)i);
    if(myClassList == null)
    {
        myClassList = new ArrayList<Object>();
        multiMap.put((double) i,myClassList);
    }
    myClassList.add("Value "+ i);
}

List<Object> myClassList = multiMap.get((double)0);
if(myClassList == null)
{
    myClassList = new ArrayList<Object>();
    multiMap.put( (double) 0,myClassList);
}
myClassList.add("Value Duplicate");
for (Map.Entry entry : multiMap.entrySet()) 
{
  System.out.println("Key = " + entry.getKey() + ", Value = " +entry.getValue());
}

#1