More than one unique key for HashMap problem (Java)

Question

This question is a continuation of this thread:

In short: To solve my problem, I want to use Map<Set<String>, String>.

However, after I sort my data entries in Excel, remove the unnecessary parameters, and the following came out:

flow content ==> content content 
flow content ==> content depth distance 
flow content ==> content depth within 
flow content ==> content depth within distance 
flow content ==> content within 
flow content ==> content within distance 

I have more than one unique key for the hashmap if that is the case. How do I go around this... anyone have any idea?

I was thinking of maybe Map<Set <String>, List <String>> so that I can do something like:

Set <flow content>, List <'content content','content depth distance','content depth within ', ..., 'content within distance'>

But because I am parsing the entries line by line I can't figure out the way how to store values of the same repeated keys (flow content) into the same list and add it to the map.

Anyone have a rough logic on how can this be done in Java?

Thanks in advance.

--EDIT:

Trying Multimap but somehow have slight problem:

public static void main(String[] args) {

    File file = new File("apriori.txt");
    Multimap<Set <String>, String> mm = HashMultimap.create();
    Set<String> s = null;
    List l = null;

    BufferedReader br = null;

    try {
            br = new BufferedReader(new FileReader(file));
            String line = "";

            while ((line = br.readLine()) != null) {
                //Regex delete only tokenize

                String[] string = line.split(";");
                System.out.println(string[0] + " " + string[1]);

                StringTokenizer st = new StringTokenizer(string[0].trim());
                while (st.hasMoreTokens()) {
                    //System.out.println(st.nextToken());
                    s = new HashSet<String>();
                    s.add(st.nextToken());
                }
                mm.put(s,string[1]);
            }

        // dispose all the resources after using them.
        br.close();
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }

    Set<String> t = new HashSet<String>();
    t.add("content");
    t.add("by");

    String str = mm.get(t).toString();
    System.out.println(str);

    for (Map.Entry<Set <String>, String> e : mm.entries()) {
        System.out.println(e);
    }
}

The apriori.txt

byte_jump ; msg 
byte_jump ; msg by 
content ; msg 
content by ; flow 
content by ; msg 
content by ; msg flow 
content by byte_jump ; msg 
content byte_jump ; by 
content byte_jump ; msg 
content byte_jump ; msg by

Apparently the output for the forloop:

[content]= msg 
[by]= flow 
[by]= msg 
[by]= msg flow 
[byte_jump]= msg 
[byte_jump]= by 
[byte_jump]= msg by 

instead of [content by]= msg flow

Why is that so? I tried and it works. But I need Set to compare the strings regardless of position. What can I do?

Answer 1

A multimap allows multiple values for a specific key.

One implementation is the various Multimaps which are provided as part of Google Collections.

Rather than coding a way to correctly store data into a Map<String, List<String>, it would probably be a better choice to go ahead and use the appropriate data structure for the job.

Answer 2

The logic is essentially:

• map to a list, as you suggest
• to put something in the map, retrieve the list that corresponds to that key
• if the list is null, create a new one and map the key to that new list
• add the item to the list

As another poster has mentioned, you could consider a standard multi-map library class such as that provided in Google Collections. (I personally would just implement it myself because it's really simple and doesn't really warrant a whole additional library in my view, but mileage varies.)

Answer 3

public static void main(String[] args) throws IOException {

    final File file = new File("apriori.txt");
    final Multimap<String, String> map = HashMultimap.create();

    final BufferedReader reader = new BufferedReader(new FileReader(file));

    while (true) {
        final String line = reader.readLine();
        if (line == null) break;
        final String[] parts = line.split(" ; ");
        map.put(parts[0].trim(), parts[1].trim());
    }

    for (Map.Entry<String, String> e : map.entries()) {
        System.out.println(e);
    }
}

Should do the trick. (I didn't compile it, no guarantees though.)
Make sure you use Multimap<String, String>, no need to use a single element set as a key there.

Answer 4

Regarding your code with MultiMap: the only thing you're doing wrong is to create a new set for every token instead of putting all the tokens of a line into the same set. That's also why you're missing tokens. This works:

s = new HashSet<String>();
while (st.hasMoreTokens()) {
    //System.out.println(st.nextToken());
    s.add(st.nextToken());
}