Usefull IEnumerable extensions: AllSame, Fold

MyExtensions.cs

public static class MyExtensions
    {
        public static T1 Fold<T1, T2>(this IEnumerable<T2> xs, Func<T1,T2,T1> func, T1 acc)
        {
            if (xs.Count() == 0) return acc;
            else return xs.Skip(1).Fold(func, func(acc, xs.First()));
        }
        public static bool AllSame<T>(this IEnumerable<T> xs)
        {
            return xs.AllSame(x => x);
        }
        public static bool AllSame<T, TSel>(this IEnumerable<T> xs, Func<T,TSel> selector)
        {
            if (xs == null) throw new ArgumentNullException(nameof(xs));
            var enumerator = xs.GetEnumerator();
            var toCompare = default(TSel);
            if (enumerator.MoveNext())
            {
                toCompare = selector(enumerator.Current);
            }
            while (enumerator.MoveNext())
            {
                if (!toCompare.Equals(selector(enumerator.Current)))
                {
                    return false;
                }
            }
            return true;
        }
    }