GroupBy_2

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication17
{
    class Program
    {
        public static IEnumerable<IEnumerable<T>> GroupBy<T, F>(IEnumerable<T> collection, Func<T, F> rule)
        {
            var dicResult = new Dictionary<F, List<T>>();
            foreach(var e in collection)
            {
                var functionValue = rule(e);
                if (!dicResult.ContainsKey(functionValue))
                {
                    dicResult.Add(functionValue, new List<T> { e});
                }
                else
                {
                    dicResult[functionValue].Add(e);
                }
            }
            return dicResult.Values ;
        }
        static void Main(string[] args)
        {
            var list = new List<string>()
            {
                "abc","bcd","d","f","gfd","2","fsdfsdfsdf","b", "gaa", "22"
            };
            Func<string, int> f = line => line.Length;
            Func<string, char> g = line => line[0];
            var result = GroupBy(list, f);
            var result2 = GroupBy(list, g);
        }
    }
}