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.

Everything is possible. Have you tried something, do you have something to show us ? And of course, can you explain what you try to check exactly. You speak about number value but I see R01018 ... not a 10-based number. — AxelH
Thanks AxelH. I want to count the number of values. The type of data is not important. Any value can be. — torochi
Do you mean you want the count of values for a key, e.g. for key 00254 the count would be the sum of 2+11+4+5+6+...? — Andreas
Per key, iterate the value and use a Map<YourValue, Integer> to count. But you need to try first. That "value" is nothing but a List, so you can simply use the same logic. See Count occurrences of words in ArrayList — AxelH
Did you read the documentation, i.e. the javadoc of Multimap? Perhaps get(key).size() is what you're looking for? — Andreas

AxelH AxelH · Accepted Answer · 2018-03-22T07:09:17

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.

Count duplicate values in Multimap

2 Answers