Data structures that can map a range of keys to a value

Question

I am trying to find a data structure that takes in a particular value from a range of values and map it to a key.

For example, I have the following conditions:

1. From 1 to 2.9, I want to map it to A.
2. From 4 to 6, I want to map it to B.
3. From 6.5 to 10, I want to map it to C.

I have a value of 5 and I would like to map it to a key. So based on the above conditions, I should map it to B.

Is there any data structure in Java that anyone can recommend to me to solve the problem?

Currently I am using a hashtable that can only map a value to a key. I tried to map the range of values to a particular value that exists in the hashtable. However, I got stuck in the mapping of the range of values to a particular value. So now I am trying to do another way of mapping the ranges of values to a key. Does anyone have any idea how I can solve this problem?

EDIT:

Thanks to Martin Ellis, I decided to use TreeMap to solve the problem.

Answer 1

Are your ranges non-overlapping? If so you could use a TreeMap:

TreeMap<Double, Character> m = new TreeMap<Double, Character>(); m.put(1.0, 'A'); m.put(2.9, null); m.put(4.0, 'B'); m.put(6.0, null); m.put(6.5, 'C'); m.put(10.0, null); 

The lookup logic is a bit complicated by the fact that you probably want an inclusive lookup (i.e. 2.9 maps to 'A', and not undefined):

private static <K, V> V mappedValue(TreeMap<K, V> map, K key) {     Entry<K, V> e = map.floorEntry(key);     if (e != null && e.getValue() == null) {         e = map.lowerEntry(key);     }     return e == null ? null : e.getValue(); } 

Example:

mappedValue(m, 5) == 'B' 

More results include:

0.9 null 1.0 A 1.1 A 2.8 A 2.9 A 3.0 null 6.4 null 6.5 C 6.6 C 9.9 C 10.0 C 10.1 null