Hashmap

[ryan12345]

I have a hashmap which currently contains people's names as keys and then has a string arraylist as the values which are the peoples currently owned cars.

For example:

Tom: BMW, Audi
John: Vauxhall
Steve: Audi, Ford

What I want to do is, is print each car's name and how many people have it as an owned car e.g. Audi: 2, BMW: 1

Any ideas of how I would do this?

Thanks.

[curmudgeon]

Nested for loops come to mind:
1 for loop to iterate through the Map
the inner one to iterate through each ArrayList.

Inside the nested for loop fill up another Map<String, Integer> to associate each car with a count.

In pseudo code

Create a Map<String, Integer> called carCountMap
Loop through all the keys of the first Map, the one with the owner/car String ArrayList
   get the associated ArrayList of Strings
   Loop through this ArrayList, getting each car String.
       Check if car String is held by carCountMap. If so, 
           get the associated Integer, increase it by one
           put it back into the carCountMap with the car String as key.
       if not, then put a new entry into the carCountMap with the car name as key and 1 as the value.
   end Loop through ArrayList.
end for loop

[ryan12345]

That's great thanks. Quick question, how would I go about looping through the associated ArrayList of Strings?

[curmudgeon]

That's great thanks. Quick question, how would I go about looping through the associated ArrayList of Strings?

Either a for loop (you know the size of the ArrayList, of course), or a for-each loop would work well here.

[ryan12345]

I've come up with this:

   public static void listCars()
    {
        for (String key : cars.keySet()) {
           for (int x=0; x < (cars.get(key)).size(); x++)
           {
               carsListed.put((cars.get(key)).get(x), +1);
            }
        }
        System.out.println(carsListed.toString());
    }

However when I call it, it doesn't seem to be adding up the amount of cars correctly.

[curmudgeon]

Please if you cross-post your question, tell all threads about the cross-post. Not informing us is not being fair to us as you then force us to duplicate answers that have already been given. We are volunteers with our own lives to lead, and we value our free time greatly. We would appreciate it if you valued our free time as well.

[ryan12345]

My apologies if I caused offence, I will do so in the future. I certainly do value your replies and advice.