java - 计算 map 中值的出现次数

Question

我有以下类型的 map :

private HashMap<Integer, HashMap<String, Object>> entireMap;

键从 1 到 n。 entireMap里面的subMap是下面的类型:

HashMap<String, Object> subMap = new HashMap<String, Object>();

整个 map 的每个键都包含这个子 map (以及更多):

subMap.put("user_name", usid[1]);

所以我最后有这样的东西:

{1 {"user_name" = "Arthur", "otherKeys = ..."}}
{2 {"user_name" = "Bela", "otherKeys = ..."}}
{3 {"user_name" = "Ceasar", "otherKeys = ..."}}
{4 {"user_name" = "Ceasar", "otherKeys = ..."}}
{5 {"user_name" = "Bela", "otherKeys = ..."}}
{6 {"user_name" = "Bela", "otherKeys = ..."}}

现在我想计算 user_name 在 entireMap 中的最大出现次数，在本例中为 3(bela occures 三次)。

我该怎么做？

Answer 1

这是一个实现示例。

注意:不要在生产代码中使用这样的 map 初始化!

    HashMap<Integer, HashMap<String, Object>> entireMap = new HashMap<>();
    entireMap.put(1, new HashMap<String, Object>() {{
        put("user_name", "Arthur");
        put("other_key1", "val");
        put("other_key2", "val");
    }});
    entireMap.put(2, new HashMap<String, Object>() {{
        put("user_name", "Bela");
        put("other_key2", "val");
    }});
    entireMap.put(3, new HashMap<String, Object>() {{
        put("user_name", "Ceasar");
    }});
    entireMap.put(4, new HashMap<String, Object>() {{
        put("user_name", "Ceasar");
    }});
    entireMap.put(5, new HashMap<String, Object>() {{
        put("user_name", "Bela");
    }});
    entireMap.put(6, new HashMap<String, Object>() {{
        put("user_name", "Bela");
    }});

    Map<Object, Long> result = entireMap
            .values()
            .stream()
            .map(map -> map.get("user_name"))
            .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));

    System.out.println(result);

    Long max = Collections.max(result.values());
    System.out.println(max);

输出:

{Ceasar=2, Arthur=1, Bela=3}
3