Question

I have a collection of user defined class object, e.g. Car instances, what is the best way to sort it.

Below are the possible ways, which one is the best, is there other ways?

1. IComparable
2. Comparer
3. Comparison
4. IEquatable

Any idea would be very much appreciated

Answer 1

There’s another important and extremely simple way, unless you absolutely require that you sort in-place: use LINQ to Objects. For example:

var orderedByName = cars.OrderBy(car => car.Name).ToList();

You can order by multiple projections, and in a varied fashion, like this:

var complex = cars.OrderByDescending(car => car.Year)
                  .ThenBy(car => car.Model)
                  .ThenByDescending(car => car.Make)
                  .ToList();

I’ve only put the ToList at the end to create a List<Car> at the end – if you only need to iterate over the results though, you can let it perform the ordering lazily:

var query = cars.OrderByDescending(car => car.Year)
                  .ThenBy(car => car.Model)
                  .ThenByDescending(car => car.Make);

foreach (var car in cars)
{
    // Use car
}

Personally I find this the most flexible way of sorting. Otherwise, using IComparer<T> and Comparison<T> are the next most flexible, as anyone can order that way. IComparable<T> requires the class itself to decide how items are going to be ordered, and you can only implement it once, which makes it somewhat inflexible.

IEquatable<T> is used for comparing items for equality, so is used for things like HashSet<T>, not for ordering.