How to perform merge sort using LINQ?

Question

Assume that you have two IEnumerbale objects. How we can merge them (in some condition e.g merge in merge sort ...) and create a unique IEnumerable

Answer 1

There is no Merge method in System.Linq.Enumerable. If you want one, you have to write it (with a for loop and a yield statement).

As with many "just by linq" questions - you should assume that every linq method is backed by some plain old .NET code that you could have written yourself.

---

Here's an untested freehand non-generic implementation

public static IEnumerable Merge
(
this IEnumerable source1,
IEnumerable source2
)
{
  using(Enumerator e1 = source1.GetEnumerator())
  {
    bool more1 = e1.MoveNext();
    using(Enumerator e2 = source2.GetEnumerator()
    {
      bool more2 = e2.MoveNext();

      while (more1 && more2)
      {
        int v1 = e1.Current;
        int v2 = e2.Current;
        if (v1 < v2)
        {
          yield return v1;
          more1 = e1.MoveNext();
        }
        else
        {
          yield return v2;
          more2 = e2.MoveNext();
        }

      }
      while (more1 && ! more2)
      {
        yield return e1.Current;
        more1 = e1.MoveNext();
      }
      while (more2 && ! more1)
      {
        yield return e2.Current;
        more2 = e2.MoveNext();
      }
    }
  }
}