Question

I have some objects:

class Foo {     public Guid id;     public string description; }  var list = new List<Foo>(); list.Add(new Foo() { id = Guid.Empty, description = 'empty' }); list.Add(new Foo() { id = Guid.Empty, description = 'empty' }); list.Add(new Foo() { id = Guid.NewGuid(), description = 'notempty' }); list.Add(new Foo() { id = Guid.NewGuid(), description = 'notempty2' }); 

I would like to process this list in such a way that the id field is unique, and throw away the non-unique objects (based on id).

The best I could come up with is:

list = list.GroupBy(i => i.id).Select(g=>g.First()).ToList(); 

Is there a nicer/better/quicker way to achieve the same result.

Answer 1

A very elegant and intention revealing option is to define a new extension method on IEnumerable

So you have:

list = list.Distinct(foo => foo.id).ToList(); 

And …

    public static IEnumerable<T> Distinct<T,TKey>(this IEnumerable<T> list, Func<T,TKey> lookup) where TKey : struct {         return list.Distinct(new StructEqualityComparer<T, TKey>(lookup));     }       class StructEqualityComparer<T,TKey> : IEqualityComparer<T> where TKey : struct {          Func<T, TKey> lookup;          public StructEqualityComparer(Func<T, TKey> lookup) {             this.lookup = lookup;         }          public bool Equals(T x, T y) {             return lookup(x).Equals(lookup(y));         }          public int GetHashCode(T obj) {             return lookup(obj).GetHashCode();         }     } 

A similar helper class can be built to compare objects. (It will need to do better null handling)