Count occurrences of value in a map

Question

I have a map of the following type:

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

The keys go from 1 - n. The subMap inside the entireMap is of the following type:

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

Every key of the entire map contains this subMap (and a lot more):

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

So i have something like this at the end:

{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 = ..."}}

Now I want to count the max occurence of a user_name in the entireMap, in this case it would be 3 (bela occures three times).

How can I do that?

Answer 1

Here is an example of an implementation.

Note: don't use such map initialization in production code!

    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);

Output:

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