How to create dictionary in c# with two keys?

Question

In C#, I want to have a data structure that maps (x,y) coordinates to (x,y). How can I do something like this?

I don't want to convert the x,y coordinate into a single value using a formula like y*w+x. Is there a way to have dictionary<key,key,(value,value)>.

If I put the key as Tuple, then its an object and Tuple(1,1) does not equal Tuple(1,1). So I don't think I can find keys in that sense.

Can't you just define (or use the pre-existing) `Point` as a structure that holds `(x, y)` and then use that in your `Dictionary`? — marc_s, Aug 07 '15 at 04:58
@omega remember if you use the System.Drawing.Point then your points coordinates should be `int`. — Hossein Narimani Rad, Aug 07 '15 at 05:25

Taher Rahgooy · Answer 1 · 2015-08-07T05:44:24.913

If you use struct rather than class the keys will be compared based on the values not based on the reference, because the structs are value type

public struct Point
{
   public int x;
   public int y;
   public Point(int x, int y)
   {
      this.x = x;
      this.y = y;
   }
 }

Then using this struct

var dic = new Dictionary<Point,Point>();
dic.Add(new Point(1,1), new Point(1,2));

var f = dic[new Point(1,1)];
Console.WriteLine(f.x); //Output will be 1

score 3 · Accepted Answer · edited Jul 09 '19 at 08:51

3

Can't you just define (or use the pre-existing structure from the System.Drawing namespace) Point as a structure that holds (x, y) and then use that in your Dictionary<Point, Point>?

edited Jul 09 '19 at 08:51

Cid

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answered Aug 07 '15 at 05:09

marc_s

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score 1 · Answer 3 · answered Aug 07 '15 at 04:59

1

var dict = new Dictionary<Point,string>();
dict[new Point(1,3)] = "asd";

answered Aug 07 '15 at 04:59

Backs

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score 1 · Answer 4 · edited May 23 '17 at 12:32

1

You can use any kind of object for as a dictionary key, as long as you correctly override GetHashCode() for that type. This is what the dictionary will use to determine whether a specific key exists in it or not. Therefore you can create your own class and use that as a key.

Check this answer for more information: What is the best algorithm for an overridden System.Object.GetHashCode?

edited May 23 '17 at 12:32

Community

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answered Aug 07 '15 at 05:03

Ioannis Karadimas

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score 1 · Answer 5 · answered Aug 07 '15 at 05:04

I'm writing this answer because the other ones seem to map to 1 string, and you need to map to 2 strings. You could try using Point to stores the x and y position and then create a dictionary of a Tuple.

var points = new Dictionary<Point,Tuple<string, string>>();
points[new Point(1,1)] = new Tuple<string, string>("2","2");

Krunal Mevada · Answer 6 · 2015-08-07T05:24:04.697

public class Point
{
    public string X {get; protected set;}
    public string Y {get; protected set;}
    public Point(string x, string y)
    {
        X = x;
        Y = y;
    }

    public HashSet<string> GetSet()
    {
        HashSet<string> result = new HashSet<string>();
        result.Add(this.X);
        result.Add(this.Y);
        return result;
    }
}

CreateSetComparer allows the dictionary to use the values of the set

List<Point> pointSource = GetSet();
Dictionary<HashSet<string>, Point> points = new Dictionary<HashSet<string>, Point>(HashSet<string>.CreateSetComparer());

foreach(Point d in pointSource)
{
    points.Add(d.GetSet(), d);
}

And finding a point:

HashSet<string> key = new HashSet<string>();
key.Add("X");
key.Add("Y");
Point myPoint = points[key];

May this link is help full HashCode

score -1 · Answer 7 · answered Aug 07 '15 at 05:08

Dictionary<string, int> dictionary =  new Dictionary<string, int>();

dictionary.Add("cat", 2);
dictionary.Add("dog", 1);
dictionary.Add("llama", 0);
dictionary.Add("iguana", -1);


if (dictionary.ContainsKey("apple"))
{
    int value = dictionary["apple"];
    Console.WriteLine(value);
}

How to create dictionary in c# with two keys?

7 Answers7