Question

I would be really grateful if you could help me with that.

Map<String, Double> movieMap = new HashMap<String, Double>;
movieMap.add("MovieA", 3);
movieMap.add("MovieB", 5);
movieMap.add("MovieC", 4);
movieMap.add("MovieD", 3.5);
movieMap.add("MovieE", 2.5);

Map<String, Double> movieMap2 = new HashMap<String, Double>;
movieMap2.add("MovieA", 3.5);
movieMap2.add("MovieB", 2.5);
movieMap2.add("MovieC", 4.5);
movieMap2.add("MovieD", 2);
            .
            .
            .
Map<String, Double> movieMapi = new HashMap<String, Double>;
movieMap2.add("MovieA", 5);
movieMap2.add("MovieC", 1.5);
movieMap2.add("MovieD", 2);

Map<String, Map<String, Double>> userMap = new HashMap<String, Map<String, Double>>;
userMap.add("Nick", movieMap);
userMap.add("Bill", movieMap2);
           .
           .
           .
userMap.add("Tom", movieMapi);

What i want to do is to make a function compare(userA, userB) and put the common movies and their rates into a new Map. By way of example the output of compare(Nick,Tom) should be a Map with keys – values : {{“MovieA”, {5,3}}, {“MovieC”, {4,1.5}}, {“MovieD”, {3.5,2}}}

It seems pretty hard for me to solve it..Can you please help me?
Thanks…

Answer 1

You can iterate over the keys in a map using the Map.keySet() method:

Set<String> nickKeys = userMap.get("Nick").keySet();
Set<String> tomKeys = userMap.get("Tom").keySet();

Your code might look something like this:

Map<String, Double> nickMap = userMap.get("Nick");
Map<String, Double> tomMap = userMap.get("Tom");

Map<String, List<Double>> commonMap = new HashMap<String, List<Double>>();

for (String movieName : nickMap.keySet()) {
    if (tomMap.containsKey(movieName)) {
        List<Double> tempList = new ArrayList<Double>();
        tempList.add(nickMap.get(movieName));
        tempList.add(tomMap.get(movieName));
        commonMap.put(movieName, tempList);
    }
}