Distinct by property of class with LINQ [duplicate]

Solution 1:

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();

Solution 2:

Use MoreLINQ, which has a DistinctBy method :)

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

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

Solution 3:

Same approach as Guffa but as an extension method:

public static IEnumerable<T> DistinctBy<T, TKey>(this IEnumerable<T> items, Func<T, TKey> property)
{
    return items.GroupBy(property).Select(x => x.First());
}

Used as:

var uniqueCars = cars.DistinctBy(x => x.CarCode);

Solution 4:

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());