Question

I am using Linq to get only unique member of a select List item. How do I return a this list…
What I have now is

    var queryResult = PatientList.Select(c => c).Distinct();
    PatientList = (List<SelectListItem>)queryResult;

I am getting a cast error on the second line. What should an enterprising young developer do?

Answer 1

Try

PatientList = queryResult.ToList();

You version uses casting, which is impossible in this case, as the query result is not a list. ToList constructs a new list, basing on the enumerable against which it is called. It does something like this:

public static List<T> ToList<T>(this IEnumerable<T> collection)
{
    return new List<T>(collection);
}

You must be sure, obviously, that PatientList elements are of type SelectListItem and be aware that Distinct() will return the different OBJECTS, but not items with different fields. I.e., if in PatientList you have two independently constructed items with equal Selected, Text and Value properties, you will still have two as a result of the Distinct() call.

Additionally, what is the reason to use Select(c => c)? It effectively does noting.