Custom intersect in lambda

Question

I would like to know if this is possible to solve using a lambda expression:

List listOne = service.GetListOne();
List listTwo = service.Ge         


        

Answer 1

You may try:

var result = listOne.Join(listTwo,
    (one) => one,
    (two) => two,
    (one, two) => one,
    new MyFooComparer());

Where MyFooComparer could look like:

class MyFooComparer : IEqualityComparer
{
    public bool Equals(Foo x, Foo y)
    {
        return x.Id == y.Id && x.someKey != y.someKey;
    }

    public int GetHashCode(Foo obj)
    {
        return obj.Id.GetHashCode();
    }
}

[UPDATE]

I was curious about the performance of Intersect vs. Join so I made a small performance comparison between my solution and @p.s.w.g.'s (listOne and listTwo have 10 items each):

var comparer = new MyFooComparer();
var sw = new Stopwatch();
sw.Start();
for (int i = 0; i < 100000; i++)
{
    var result1 = listOne.Intersect(listTwo, comparer).ToList();
}
Console.WriteLine("Intersect: {0}",sw.Elapsed);
sw.Restart();
for (int i = 0; i < 100000; i++)
{
    var result = listOne.Join(listTwo,
        (one) => one,
        (two) => two,
        (one, two) => one,
        comparer);
}
Console.WriteLine("Join:      {0}", sw.Elapsed);

The output:

Intersect: 00:00:00.1441810
Join:      00:00:00.0037063