Distinct.Any

program.cs

using System;
using System.Diagnostics;
using System.Linq;
using System.Threading;

namespace DistinctAny
{
    class Program
    {
        static void Main(string[] args)
        {
            var evaluation = "A";

            var stw = Stopwatch.StartNew();
            Console.WriteLine("Start Y1");
            var y1 = new[] { "A", "A", "A", "A", "B" }
                .Any(i =>
                {
                    Thread.Sleep(1000);
                    return i == evaluation;
                });
            Console.WriteLine("Y1 completed {0}", stw.ElapsedMilliseconds);

            stw.Restart();
            Console.WriteLine("Start Y2");
            var y2 = new[] { "A", "A", "A", "A", "B" }
                .Distinct()
                .Any(i =>
                {
                    Thread.Sleep(1000);
                    return i == evaluation;
                });
            Console.WriteLine("Y2 completed {0}", stw.ElapsedMilliseconds);

            Console.ReadKey();
        }
    }
}

        static void Main(string[] args)
        {
            var testData = Enumerable.Range(1, 10000000)
                .Append(0);

            long initialMemory = GC.GetTotalMemory(false);

            Console.WriteLine("Without Distinct");
            var stw = Stopwatch.StartNew();
            var y1 = testData.Any(i => i == 0);
            stw.Stop();
            long step1Memory = GC.GetTotalMemory(false);
            Console.WriteLine("Y1 completed {0}ms", stw.ElapsedMilliseconds);
            Console.WriteLine("Memory increase {0}kB", (step1Memory - initialMemory)/1024);

            Console.WriteLine("----------");
            Console.WriteLine("With Distinct");
            stw.Restart();
            var y2 = testData.Distinct().Any(i => i == 0);
            stw.Stop();
            long step2Memory = GC.GetTotalMemory(false);
            Console.WriteLine("Y2 completed {0}ms", stw.ElapsedMilliseconds);
            Console.WriteLine("Memory increase {0}kB", (step2Memory - step1Memory)/1024);

            Console.ReadKey();
        }

Output:

Without Distinct
Y1 completed 399ms
Memory increase 8kB
----------
With Distinct
Y2 completed 994ms
Memory increase 458688kB