public static class CollectionExtensions
{
    public static SelectList ToSelectList<T>(this IEnumerable<T> list,
                                             Func<T, string> value,
                                             Func<T, string> text)
    {
        return new SelectList(list.Select(x => new { Value = value(x), Text = text(x) }), "Value", "Text");
    }
 
    public static SelectList ToSelectList<T>(this IEnumerable<T> list,
                                             Func<T, string> value,
                                             Func<T, string> text,
                                             string firstValue,
                                             string firstText)
    {
        var firstSelectListItem = new { Value = firstValue, Text = firstText };
 
        var collection = (new[] { firstSelectListItem })
            .Concat(list.Select(x => new { Value = value(x), Text = text(x) }));
 
        return new SelectList(collection, "Value", "Text");
    }
 
    public static SelectList ToSelectList<T>(this IEnumerable<T> list,
                                             Func<T, string> value,
                                             Func<T, string> text,
                                             string selectedValue)
    {
        return new SelectList(list.Select(x => new { Value = value(x), Text = text(x) }), "Value", "Text", selectedValue);
    }
 
    public static SelectList ToSelectList<T>(this IEnumerable<T> list,
                                             Func<T, string> value,
                                             Func<T, string> text,
                                             string firstValue,
                                             string firstText,
                                             string selectedValue)
    {
        var firstSelectListItem = new { Value = firstValue, Text = firstText };
 
        var collection = (new[] { firstSelectListItem })
            .Concat(list.Select(x => new { Value = value(x), Text = text(x) }));
 
        return new SelectList(collection, "Value", "Text", selectedValue);
    }
 
    public static MultiSelectList ToMultiSelectList<T>(this IEnumerable<T> list,
                                                       Func<T, string> value,
                                                       Func<T, string> text,
                                                       IEnumerable<string> selectedValues)
    {
        return new MultiSelectList(list.Select(x => new { Value = value(x), Text = text(x) }), "Value", "Text", selectedValues);
    }
}