Filtering lists using LINQ

Question

I\'ve got a list of People that are returned from an external app and I\'m creating an exclusion list in my local app to give me the option of manually removing people from the

Answer 1

I couldn't figure out how to do this in pure MS LINQ, so I wrote my own extension method to do it:

public static bool In<T>(this T objToCheck, params T[] values)
{
    if (values == null || values.Length == 0) 
    {
        return false; //early out
    }
    else
    {
        foreach (T t in values)
        {
            if (t.Equals(objToCheck))
                return true;   //RETURN found!
        }

        return false; //nothing found
    }
}

Answer 2

This LINQ below will generate the SQL for a left outer join and then take all of the results that don't find a match in your exclusion list.

List<Person> filteredResults =from p in people
        join e in exclusions on p.compositeKey equals e.compositeKey into temp
        from t in temp.DefaultIfEmpty()
        where t.compositeKey == null
        select p

let me know if it works!

Answer 3

I would do something like this but i bet there is a simpler way. i think the sql from linqtosql would use a select from person Where NOT EXIST(select from your exclusion list)

static class Program
{
    public class Person
    {
        public string Key { get; set; }
        public Person(string key)
        {
           Key = key;
        }
    }
    public class NotPerson
    {
        public string Key { get; set; }
        public NotPerson(string key)
        {
           Key = key;
        }
    }
    static void Main()
    {

       List<Person> persons = new List<Person>()
       { 
           new Person ("1"),
           new Person ("2"),
           new Person ("3"),
           new Person ("4")
       };

       List<NotPerson> notpersons = new List<NotPerson>()
       { 
           new NotPerson ("3"),
           new NotPerson ("4")
       };

       var filteredResults = from n in persons
                             where !notpersons.Any(y => n.Key == y.Key)
                             select n;

       foreach (var item in filteredResults)
       {
          Console.WriteLine(item.Key);
       }
    }
 }