Is there an AddUnique method similar to Addrange() for alist in C#

Question

I have a list in C#:

       var list = new List();
       list.AddRange(GetGreenCars());
       list.AddRange(GetBigCars());
       list.AddRange(         


        

Answer 1

Given you override the .Equals() method for Car to determine one car object is the same as another car object, then the following should work w/o writing an extension method.

    var list = new List<Car>();
    list.AddRange(GetGreenCars()?.Except(list) ?? new List<Car>());
    list.AddRange(GetBigCars()?.Except(list) ?? new List<Car>());
    list.AddRange(GetSmallCars()?.Except(list) ?? new List<Car>());

Answer 2

A List<T> doesn't seem to be the appropriate collection here. You probably want an ISet<T> implementation such as HashSet<T> (or SortedSet<T> if you need ordering).

To allow this, you will need to write an IEqualityComparer<T> implementation that defines equality between cars according to the Name property. If this is the 'canonical' definition of car-equality, you can also consider directly building this definition into the Car type itself (object.Equals, object.GetHashCode and ideally implement IEquatable<T> too).

Answer 3

Assuming your Get*Cars() return Lists of Car, another option could be:

var list = new List<Car>();
GetGreenCars().ForEach(c => { if (!list.Contains(c)) list.Add(c); });
GetBigCars().ForEach(c => { if (!list.Contains(c)) list.Add(c); });
GetSmallCars().ForEach(c => { if (!list.Contains(c)) list.Add(c); });