Filtering enum values by a set of strings we want to display, with full type information.

enum.cs

// Some enum, could be RateFamilyTypes
enum Letters { A, B, C}

void Main()
{
    // List of stringified subset of enum values; could be sourced from XAML
    HashSet<string> filterList = new HashSet<string>() { "B" };

    // Get as typesafe array of enum values (allLetters is an array of Letters)
    var letterArray = Enum.GetValues(typeof(Letters));
    Letters[] allLetters = new Letters[letterArray.Length];
    letterArray.CopyTo(allLetters, 0);

    // Get an IEnumerable or Array of typed enum values, based on the filter list
    var filteredList = allLetters.Where(x => filterList.Contains(x.ToString())).ToArray();
    // Display in dropdown with full type information (filteredList is also an array of Letters)
}