LINQ's Distinct() on a particular property

Question

I am playing with LINQ to learn about it, but I can\'t figure out how to use Distinct when I do not have a simple list (a simple list of integers is pretty easy

Answer 1

Personally I use the following class:

public class LambdaEqualityComparer : 
    IEqualityComparer
{
    private Func _selector;

    public LambdaEqualityComparer(Func selector)
    {
        _selector = selector;
    }

    public bool Equals(TSource obj, TSource other)
    {
        return _selector(obj).Equals(_selector(other));
    }

    public int GetHashCode(TSource obj)
    {
        return _selector(obj).GetHashCode();
    }
}

Then, an extension method:

public static IEnumerable Distinct(
    this IEnumerable source, Func selector)
{
    return source.Distinct(new LambdaEqualityComparer(selector));
}

Finally, the intended usage:

var dates = new List() { /* ... */ }
var distinctYears = dates.Distinct(date => date.Year);

The advantage I found using this approach is the re-usage of LambdaEqualityComparer class for other methods that accept an IEqualityComparer. (Oh, and I leave the yield stuff to the original LINQ implementation...)