Count duplicate values in Multimap

Question

I have Multimap. Example:

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]

I want to get the number of value including duplicate value.

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

Is it possible to get duplicate number?

Thanks.

Answer 1

Solution using Java 8 Stream to get the occurrence for a specific value, simply get the Collection for a value, then group on the value and count (using the Collectors function) to get a 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}

This will generate a String, I let you adapt for your need.