I wish to have the dictionary which uses an array of integers as keys, and if the integer array has the same value (even different object instance), they will be treated as the same key. How should I do it?
The following code does not work as b is different object instances.
int[] a = new int[] { 1, 2, 3 };
int[] b = new int[] { 1, 2, 3 };
Dictionary<int[], string> dic = new Dictionary<int[], string>();
dic.Add(a, "haha");
string output = dic[b];
You can create an IEqualityComparer to define how the dictionary should compare items. If the ordering of items is relevant, then something like this should work:
public class MyEqualityComparer : IEqualityComparer<int[]>
{
public bool Equals(int[] x, int[] y)
{
if (x.Length != y.Length)
{
return false;
}
for (int i = 0; i < x.Length; i++)
{
if (x[i] != y[i])
{
return false;
}
}
return true;
}
public int GetHashCode(int[] obj)
{
int result = 17;
for (int i = 0; i < obj.Length; i++)
{
unchecked
{
result = result * 23 + obj[i];
}
}
return result;
}
}
Then pass it in as you create the dictionary:
Dictionary<int[], string> dic
= new Dictionary<int[], string>(new MyEqualityComparer());
Note: calculation of hash code obtained here: What is the best algorithm for an overridden System.Object.GetHashCode?
Dictionary<,> maintains a hash table of its keys, and therefore it is necessary to have a GetHashCode that respects the new Equals. For the same reason, the IEqualityComparer<> interface requires you to do GetHashCode.
My EqualityComparer? The fact that it's yours is irrelevant. It should be called IntArrayEqualityComparer or something similar :)
x.Equals(y) then x.GetHashCode() == y.GetHashCode() must also be true. Using obj.GetHashCode() will not fulfill that promise because you have a custom implementation of Equals you will be using for the comparisons so you will end up with x.Equals(y) == true and x.GetHashCode() != y.GetHashCode() which is illegal in a correct hashcode implementation..Maybe you should consider using a Tuple
var myDictionary = new Dictionary<Tuple<int,int>, string>();
myDictionary.Add(new Tuple<int,int>(3, 3), "haha1");
myDictionary.Add(new Tuple<int,int>(5, 5), "haha2");
According to MSDN , Tuple objects Equals method will use the values of the two Tuple objects
The easiest way if you don't care about actual hashing may just be to convert the array into a string. Adding a space to avoid numbers joining.
dic.Add(String.Join(" ",a), "haha");
List<int>