Merging two IEnumerables

Question

I have two IEnumerables.

One gets filled with the fallback ellements. This one will always contain the most elements. The other one will get fi

Answer 1

use Concat. Union does not work in case List<dynamic> type

Answer 2

Try this.

public static IEnumerable<Person> SmartCombine(IEnumerable<Person> fallback, IEnumerable<Person> translated) {
  return translated.Concat(fallback.Where(p => !translated.Any(x => x.id.equals(p.id)));
}

Answer 3

translated.Union(fallback)

or (if Person doesn't implement IEquatable<Person> by ID)

translated.Union(fallback, PersonComparer.Instance)

where PersonComparer is:

public class PersonComparer : IEqualityComparer<Person>
{
    public static readonly PersonComparer Instance = new PersonComparer();

    // We don't need any more instances
    private PersonComparer() {}

    public int GetHashCode(Person p)
    {
        return p.id;
    }

    public bool Equals(Person p1, Person p2)
    {
        if (Object.ReferenceEquals(p1, p2))
        {
            return true;
        }
        if (Object.ReferenceEquals(p1, null) ||
            Object.ReferenceEquals(p2, null))
        {
            return false;
        }
        return p1.id == p2.id;
    }
}