Question

I have a question using these same examples – this question is focused on a different issue.
Given the following classes:

   [XmlRoot]
   public class Family {

      [XmlElement]
      public List<Person> Person;
   }

   public class Person {

      [XmlAttribute("member")]
      public MemberType Member { get; set; }

      [XmlAttribute("id")]
      public int Id { get; set; }

      [XmlElement]
      public string Surname { get; set; }

      [XmlElement]
      public string Forename { get; set; }

      [XmlElement("Person")]
      public List<Person> People;
   }

   public enum MemberType {
      Father,
      Mother,
      Son,
      Daughter
   }

If Family has a method defined as such:

public IEnumerable<Person> Find (Func<Person, bool> predicate) {
    //  how do I get SelectMany to flatten the list?
    foreach (var p in family.Person.SelectMany(p => p)) {
        if(predicate(p)) {
            yield return p;
        }
    }
}

I need to be able to execute the predicate over a flattened list of Person. In the example above SelectMany is not flattening the list as I had hoped. The above actually won’t compile because the inferred type cannot be determined.

How can I get the Family.Person collection to become one flattened list of Person?

Answer 1

public IEnumerable<Person> Find(IEnumerable<Person> input, Func<Person, bool> predicate) {
    return input.Select(p => 
        {
            var thisLevel = new List<Person>();
            if(predicate(p))
                thisLevel.Add(p);

            return thisLevel.Union(Find(p.People ?? new List<Person>(), predicate));
        }
    ).SelectMany(p => p);
}