MapBetween (on Zip Method)

Program.cs

using System;
using System.Linq;
using System.Collections.Generic;

namespace ConsoleApplication1
{
  public static class EnumerableEx
  {
    public static IEnumerable<TResult> MapBetween<TValue, TResult>(this IEnumerable<TValue> source, Func<TValue, TValue, TResult> f)
    {
      return source
        .Zip(
          source.Skip(1),
          (x, y) => new { OldValue = x, NewValue = y })
        .Select(x => f(x.OldValue, x.NewValue));
    }
  }

  public class Program
  {
    public static void Main(string[] args)
    {
      var q = new[] { 1, 2, 3, 4, 5 }.MapBetween((a, b) => a + b);
      foreach (var n in q)
      {
        Console.WriteLine(n);
      }
    }
  }
}