public static IEnumerable <T> StartsWith <T>(this IEnumerable <T> source, Func <T, string> selector, string from, string to = null)
{
if (!source.HasItems())
{
return(new List <T>());
}
var lowerCaseFrom = from.ToLowerInvariant()[0];
var upperCaseFrom = from.ToUpperInvariant()[0];
if (!String.IsNullOrWhiteSpace(to))
{
var lowerCaseTo = to.ToLowerInvariant()[0];
var upperCaseTo = to.ToUpperInvariant()[0];
return(source.Where(m => (selector(m)[0] >= lowerCaseFrom && selector(m)[0] <= lowerCaseTo) ||
(selector(m)[0] >= upperCaseFrom && selector(m)[0] <= upperCaseTo)));
}
return(source.Where(m => selector(m)[0] == lowerCaseFrom || selector(m)[0] == upperCaseFrom));
}