Java- Adding unique values to Hashmap

Question

ok,

here is my issue....I have a List<short>letterList which has for example: "1,2,3,4,5,6,7,8,9,10"

What Im doing is Im iterating over this list then passing the value into another method which returns a value:

so:

string value = null;
for(Short foo : letterList)

{
   value = getSomeValue(foo) //returns a letter A or B or C
}

What Im trying to do is get a hashmap to look something like this:

key: a, value 1,5,7
key b, value: 2,3,4
key c, value: 6,8,9,10

not these values specifically, but you get my point

Im not sure how to do this I have tried creating a map with a <set<string>, List<short>

any suggestions would be appreciated

You can use Map<Character, List<Short>>. If you use strings for keys, then just change Character to String. — Eldar
– Eldar, Commented Aug 12, 2013 at 20:51

John Starich · Accepted Answer · 2013-08-12 20:50:37Z

2

HashMap<Character, List<Short>> map

My understanding was you were looking for a simple way to store a list of values with a character? If so, use that above.

If you want to sort by letter (for easy printing out) use the following:

TreeMap<Character, List<Short>> map

You can get and of the values by using map.get('A') and using your standard methods to iterate through or get a certain value from the associated list.

answered Aug 12, 2013 at 20:50

John Starich

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Comments

user · Accepted Answer · 2013-08-16 07:22:17Z

1

Java has no built-in MultiMap, but you can either simulate a multimap (Map<String, List<Short>>) or try out Guava for example: https://code.google.com/p/guava-libraries/

edited Aug 16, 2013 at 7:22

answered Aug 12, 2013 at 20:45

user

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1 Comment

Doc Holiday Over a year ago

Im using Multimap<Short, Short> myMultimap = ArrayListMultimap.create();

Xabster · Accepted Answer · 2013-08-12 20:45:03Z

0

Map<String, List<Short>>

The key (String) will be unique. The List<> will be able to hold a list of shorts.

If you want to make sure the numbers are unique as well as the keys, then use a Set instead of a list.

Remember to initialize the lists you put in the map (getting a key like "A" for the first time will return null, so check if it's null and if it is then create a List, put your value into it, and put the list into the map).

answered Aug 12, 2013 at 20:45

Xabster

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Comments

rnk · Accepted Answer · 2013-08-12 20:55:44Z

0

Not knowing your complete use case, I would suggest having a different look at your data structure organization. e.g.

Map<Integer, String> map = new HashMap<Integer, String>();

Where the keys are 1,2....10 as in your example and the values are

1 -> a
2 -> b
3 -> b
etc.

To get your original "list" you can use -

Set<Integer>  numbers = map.keySet();

answered Aug 12, 2013 at 20:55

rnk

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2 Comments

Doc Holiday Over a year ago

you have it reverse..the letters that come out of the method are the keys

rnk Over a year ago

Yes I am suggesting that he actually reverse his data structure, that will be much faster lookup.

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