A dictionary object that uses ranges of values for keys

Question

I have need of a sort of specialized dictionary. My use case is this: The user wants to specify ranges of values (the range could be a single point as well) and assign a v

Answer 1

I would make a little Interval class, which would something like that:

public class Interval
{
    public int Start {get; set;}
    public int End {get; set;}
    public int Step {get; set;}
    public double Value {get; set;}

    public WriteToDictionary(Dictionary<int, double> dict)
    {
        for(int i = Start; i < End; i += Step)
        {
            dict.Add(i, Value);
        }
    }
}

So you still can a normal lookup within your dictionary. Maybe you should also perform some checks before calling Add() or implement some kind of rollback if any value is already within the dictionary.

Answer 2

You can find a Java flavored C# implementation of an interval tree in the Open Geospatial Library. It needs some minor tweaks to solve your problem and it could also really use some C#-ification.

It's Open Source but I don't know under what license.

Answer 3

A dictionary is not the appropriate data structure for the operations you are describing.

If the intervals are required to never overlap then you can just build a sorted list of intervals and binary search it.

If the intervals can overlap then you have a more difficult problem to solve. To solve that problem efficiently you'll want to build an interval tree:

http://en.wikipedia.org/wiki/Interval_tree

This is a well-known data structure. See "Introduction To Algorithms" or any other decent undergraduate text on data structures.

Answer 4

I have solved a similar problem by ensuring that the collection is contiguous where the intervals never overlap and never have gaps between them. Each interval is defined as a lower boundary and any value lies in that interval if it is equal to or greater than that boundary and less than the lower boundary of the next interval. Anything below the lowest boundary is a special case bin.

This simplifies the problem somewhat. We also then optimized key searches by implementing a binary chop. I can't share the code, unfortunately.

Answer 5

i adapted some ideas for Dictionary and func, like "ChaosPandion" gave me the idea in his earlier post here above. i still solved the coding, but if i try to refactor
i have a amazing problem/bug/lack of understanding:

Dictionary<Func<string, double, bool>, double> map = new Dictionary<Func<string, double, bool>, double>()
{
        { (a, b) => a == "2018" && b == 4, 815.72},
        { (a, b) => a == "2018" && b == 6, 715.72}
};

What is does is, that i call the map with a search like "2018"(year) and 4(month), which the result is double value 815,72. When i check the unique map entries they look like this:

map working unique keys

so thats the orginal behaviour, anything fine so far. Then i try to refactor it, to this:

Dictionary<Func<string, double, bool>, double> map = 
new Dictionary<Func<string, double, bool>, double>();

WS22(map, values2018, "2018");



private void WS22(Dictionary<Func<string, double, bool>, double> map, double[] valuesByYear, string strYear)
{
          int iMonth = 1;


             // step by step this works:
             map.Add((a, b) => (a == strYear) && (b == 1), dValue);
             map.Add((a, b) => (a == strYear) && (b == 2), dValue);



           // do it more elegant...
           foreach (double dValue in valuesByYear)
           {

             //this does not work: exception after second iteration of foreach run
              map.Add((a, b) => (a == strYear) && (b == iMonth), dValue );
              iMonth+=1; 
          }
}

this works: (i use b==1 and b==2)

this does not work (map not working exception on add item on second iteration)

so i think the problem is, that the map does not have a unique key while adding to map dictionary. The thing is, i dont see my error, why b==1 is working and b==iMonth not.

Thx for any help, that open my eyes :)

Answer 6

You could check out the powercollections here found on codeplex that has a collection that can do what you are looking for.

Hope this helps, Best regards, Tom.