Distinct() with lambda?

Question

Right, so I have an enumerable and wish to get distinct values from it.

Using System.Linq, there\'s of course an extension method called Distinct<

Answer 1

No there is no such extension method overload for this. I've found this frustrating myself in the past and as such I usually write a helper class to deal with this problem. The goal is to convert a Func to IEqualityComparer.

Example

public class EqualityFactory {
  private sealed class Impl : IEqualityComparer {
    private Func m_del;
    private IEqualityComparer m_comp;
    public Impl(Func del) { 
      m_del = del;
      m_comp = EqualityComparer.Default;
    }
    public bool Equals(T left, T right) {
      return m_del(left, right);
    } 
    public int GetHashCode(T value) {
      return m_comp.GetHashCode(value);
    }
  }
  public static IEqualityComparer Create(Func del) {
    return new Impl(del);
  }
}

This allows you to write the following

var distinctValues = myCustomerList
  .Distinct(EqualityFactory.Create((c1, c2) => c1.CustomerId == c2.CustomerId));