Question

I have two generic lists. Let’s say they are List< A > and List< B >.

ClassA has a property, which type is List< B >. This property contains B type objects, which are filtered by some other proerties of object A.

So:

class A{
  public int Something1;
  public int Something2;
  public List<B> Something3;
}

class B{
  public int Anything1;
  public int Anything2;
}

I’d like to add all object B as a list to object A (to Property called Something3), where let’s say object A.Something1 == B.Anything1.

My question is: what is the most efficient way of adding List<B> items to List<A> items? Note, there can be hundreds of thousands of objects in both lists.

(VS2010; C#; .Net4)

Answer 1

Group the B‘s on the Anything1 property and put in a dictionary. Then you can loop through the A‘s and efficiently pick out the list of B‘s:

Dictionary<int, List<B>> beegroups = bees.GroupBy(b => b.Anything1).ToDictionary(g => g.Key, g => g.ToList());

foreach (A a in ayes) {
  List<B> group;
  if (beegroups.TryGetValue(a.Something1, out group)) {
    a.Something3 = group;
  }
}