Question

I would like to store data in Generic Dictionary with keys that match over Date Ranges.

For instance, I came up with the following idea

public class MyKey : IEquatable<MyKey> 
{
  public int Key { get; set; }
  public DateTime StartDate { get; set; }
  public DateTime EndDate { get; set; }

  public override int GetHashCode() 
  { 
    returns Key;
  }

  // if there is overlap in date range consider them equal
  public bool Equals(MyKey other)
  {
    if (Key!=other.Key)
      return false;
    else if(other.StartDate >=StartDate && other.StartDate <=EndDate) 
      return true;
    else if(other.EndDate >=StartDate && other.EndDate <=EndDate) 
      return true;
    else if(StartDate >=other.StartDate && StartDate <=other.EndDate) 
      return true;
    else if(EndDate >=other.StartDate && EndDate <=other.EndDate) 
      return true;
    else
      return false;
  }
}

Then the I would use a Dictionary as so

var dict = new Dictionary<MyKey,MyClass>();
Populate(dict);

// get an element where the current date is in the daterange of the key
// in the collection
var key = new MyKey();
key.Key=7;
key.StartDate=DateTime.Now;
key.EndDate=key.StartDate;

// retrieve the matching element for the date
var myclass = dict[key];

This was the best I could come up with, however it seems kludgy way to do this. I thought of adding a fourth property called selection date. And would set that to null in the entries in the dictionary but would use it during lookups in the Equals method.

I am wondering if anyone else has come up with an elegant solution to this problem?

I should mention that I will be matching on the key first and then there could be date ranges for the specific key property.

Answer 1

For getHashCode return a hash of this.StartDate and this.EndDate and this.Key. See this page for simple hashing ideas. There are better hashing methods out there but that page should get you started.

Add a static method that takes in a int key and a single DateTime as it seems that is how you are using this. (this could take in two DateTimes for a range if you need it)
return myDictionary[myDictionary.Keys.Find(x=> value < x.EndDate && value > x.StartDate) && x.Key = key];

For two dates:
return myDictionary[myDictionary.Keys.Find(x=> ((date1 < x.EndDate && date1 > x.StartDate)) || (date2 < x.EndDate && date2 > x.StartDate))) && x.Key = key];

Either of these could be made a find all if you are using a range as there may be collisions.

Change your equals conditions to just

return this.StartDate.Equals(o.StartDate) && this.EndDate.Equals(o.EndDate) && this.Key.Equals(o.Key);

Using the above static method you no longer need the concept of overlapping keys.