Distinct by property of class by linq

Question

I have a collection:

List<Car> cars=new List<Car>

Cars are uniquely identified by CarCode.

I have three cars in the collection, and two with identical CarCodes.

How can I use LINQ to convert this collection to Cars with unique CarCodes?

Answer 1

Use MoreLINQ, which has a DistinctBy method :)

IEnumerable<Car> distinctCars = cars.DistinctBy(car => car.CarCode);

(This is only for LINQ to Objects, mind you.)

Answer 2

You can use grouping, and get the first car from each group:

List<Car> distinct =
  cars
  .GroupBy(car => car.CarCode)
  .Select(g => g.First())
  .ToList();

Answer 3

You can implement an IEqualityComparer and use that in your Distinct extension.

class CarEqualityComparer : IEqualityComparer<Car>
{
    #region IEqualityComparer<Car> Members

    public bool Equals(Car x, Car y)
    {
        return x.CarCode.Equals(y.CarCode);
    }

    public int GetHashCode(Car obj)
    {
        return obj.CarCode.GetHashCode();
    }

    #endregion
}

And then

var uniqueCars = cars.Distinct(new CarEqualityComparer());