/// <summary>
/// Returns the values in a sequence whose resulting value of the specified 
/// selector is between the lowest and highest values given in the parameters.
/// </summary>
/// <typeparam name="TSource">
/// The type of elements in the sequence.
/// </typeparam>
/// <param name="source">
/// The IEnumerable object on which this method works.
/// </param>
/// <param name="selector">
/// The selector predicate used to attain the value.
/// </param>
/// <param name="lowest">
/// The lowest value of the selector that will appear in the new list.
/// </param>
/// <param name="highest">
/// The hightest value of the selector that will appear in the new list.
/// </param>
/// <returns>
/// An IEnumerable sequence of TSource whose selector values fall within the range 
/// of <paramref name="lowest"/> and <paramref name="highest"/>.
/// </returns>
public static IEnumerable<TSource> Between<TSource, TResult>
(
    this IEnumerable<TSource> source, Func<TSource, TResult> selector,
    TResult lowest, TResult highest
)
    where TResult : IComparable<TResult>
{
    return source.OrderBy(selector).
        SkipWhile(s => selector.Invoke(s).CompareTo(lowest) < 0).
        TakeWhile(s => selector.Invoke(s).CompareTo(highest) <= 0 );
}
 
/// <summary>
/// This is a simple test for the Between Linq extension method. We'll add a few
/// values to a list and select only those that are between a certain range.
/// When we're done, we should know the lowest and highest values contained
/// in the resulting values set.
/// </summary>
[TestMethod]
public void BetweenTest()
{
    var list = new List<double>();
    for (var i = 1; i <= 20; i++)
        list.Add(i);
    var fiveTo15 = list.Between(s => s, 5, 15);
    Assert.IsTrue(fiveTo15.Min() == 5);
    Assert.IsTrue(fiveTo15.Max() == 15);
}