计算 Multimap 中的重复值

Question

我有Multimap。示例：

00254=[00255, 2074E, 2074E, 2074E, 2074E, 2074E, 2074E, 00010, 00010, 00010, 0006, 0006, 0006, 00010, R01018, R01018, 0006, 0006, R01018, R01018, R01018, 12062, S2202962, S2202962, R01018, 12062, 20466, 12062, 20466, 22636, 20466, 20466, 22636, 22636, 22636, 22636, 22636, 22636, 22636, 22636, 00255, 2074E, 2074E, 2074E, 2074E, 2074E]
00256=[00257, 2074E, 2074E, 2074E, 2074E, 00010, 2074E, 2074E, 0006, 00010, 00010, 00010, 0006, 0006, 0006, R01018, R01018, 0006, R01018, R01018, R01018, 12062, S2202962, S2202962, R01018, 12062, 20466, 12062, 20466, 20466, 20466, 22636, 22636, 22636, 22636, 22636, 22636, 22636, 22636, 22636, 00257, 2074E, 2074E, 2074E, 2074E, 00010]

我想获取包含重复值的值的个数。

00254=[00255:2, 2074E:11, 00010:4, 0006:5, R01018:6, ...]
00256=[00257:2, 2074E:10, 00010:5, 0006:5, R01018:7, ...]

是否可以得到重复的号码？

谢谢。

Answer 1

解决方案使用 Java 8 Stream 获取特定值的出现，只需获取值的 Collection，然后对值进行分组并计数（使用 Collectors函数）得到一个 Map<String, Long> :

Multimap<Integer, String> maps =  ArrayListMultimap.create();
maps.put(1, "foo");
maps.put(1, "bar");
maps.put(1, "foo");
maps.put(2, "Hello");
maps.put(2, "foo");
maps.put(2, "World");
maps.put(2, "World");

Here is the idea to print the occurences per value :

maps.keySet().stream() //Iterate the `keys`
            .map(i -> i + " : " +  //For each key
                        maps.get(i).stream() //stream the values.
                            .collect( //Group and count
                                    Collectors.groupingBy(
                                            Function.identity(), 
                                            Collectors.counting()
                                    )
                            )
            )
            .forEach(System.out::println);

1 : {bar=1, foo=2}

2 : {Hello=1, foo=1, World=2}

这会生成一个String，我让你根据自己的需要进行调整。

Answer 2

计算出现次数是 Multiset 的完美用例，即

A collection that supports order-independent equality, like Set, but may have duplicate elements. A multiset is also sometimes called a bag.

Elements of a multiset that are equal to one another are referred to as occurrences of the same single element.

几乎没有什么不同 Multiset implementations you can choose from, and couple of handy set-like methods in Multisets helper class。

在这里，您可以 1) 收集到 multiset 或 2) 使用具有 multiset 值的自定义 multimap。

您可以收集不可变的多重集，而不是分组映射：

ImmutableMultiset<String> qtyMultiset = multimap.get(key).stream()
    .collect(ImmutableMultiset.toImmutableMultiset());

或可变的：

HashMultiset<String> qtyMultiset = multimap.get(key).stream()
    .collect(Multisets.toMultiset(Function.identity(), e -> 1, HashMultiset::create));

或者您可以首先使用自定义多图？（不幸的是，没有任何 MultisetMultimap 接口或实现，因此需要自定义实例）：

Multimap<String, String> countingMultimap
    = Multimaps.newMultimap(new LinkedHashMap<>(), LinkedHashMultiset::create);

如果不需要保留顺序，可以删除 Linked 部分。对于您的数据：

countingMultimap.putAll("00254", ImmutableList.of("00255", "2074E", "2074E", "2074E", "2074E", "2074E", "2074E", "00010", "00010", "00010", "0006", "0006", "0006", "00010", "R01018", "R01018", "0006", "0006", "R01018", "R01018", "R01018", "12062", "S2202962", "S2202962", "R01018", "12062", "20466", "12062", "20466", "22636", "20466", "20466", "22636", "22636", "22636", "22636", "22636", "22636", "22636", "22636", "00255", "2074E", "2074E", "2074E", "2074E", "2074E"));
countingMultimap.putAll("00256", ImmutableList.of("00257", "2074E", "2074E", "2074E", "2074E", "00010", "2074E", "2074E", "0006", "00010", "00010", "00010", "0006", "0006", "0006", "R01018", "R01018", "0006", "R01018", "R01018", "R01018", "12062", "S2202962", "S2202962", "R01018", "12062", "20466", "12062", "20466", "20466", "20466", "22636", "22636", "22636", "22636", "22636", "22636", "22636", "22636", "22636", "00257", "2074E", "2074E", "2074E", "2074E", "00010"));

返回的多图将是：

{00254=[00255 x 2, 2074E x 11, 00010 x 4, 0006 x 5, R01018 x 6, 12062 x 3, S2202962 x 2, 20466 x 4, 22636 x 9], 00256=[00257 x 2, 2074E x 10, 00010 x 5, 0006 x 5, R01018 x 6, 12062 x 3, S2202962 x 2, 20466 x 4, 22636 x 9]}

有关详细信息，请阅读 Guava Wiki page about Multiset（以字数统计为例）。

计算 Multimap 中的重复值

Count duplicate values in Multimap

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