Count number of element in List>

Question

I have a List>. How can I count all the elements in this as if it was a single List in the fastest way?

So far I h

Answer 1

I'd like to get the chance to answer this question just to highlight when we should use linq and when a classic for. Unfortunately today people doesn’t care a lot about performance as we got use to work on very powerful computer. Anyway just try the code below and you will discover that Linq is more then 100 times slower than the classic for version. You should use Linq only when the expression you need to write is really complex and you want make it more readable. I didn't spend time to the solution shoed below as I'd like to focus on the performance

public static void Main(string [] arg)
{
    //create the list
    List> listOfList = new List>()
                                      {
                                          new List()
                                              {
                                                  "1.1","2.2"
                                              }
                                      ,
                                       new List()
                                              {
                                                  "2.1","2.2","2.3"
                                              }
                                      };
    //stopwatch using Linq
    Stopwatch stopwatch=new Stopwatch();
    stopwatch.Start();

    int totalUsingLinq = listOfList.Sum(x => x.Count);

    stopwatch.Stop();
    Console.WriteLine("Using Linq:{0}",stopwatch.Elapsed); //00005713

    int totalUsingFor = 0;
    //stopwatch using classic for 
    stopwatch.Reset();
    stopwatch.Start();
    totalUsingFor = 0;
    for(int i=0;i

distinct version using for (just for example). In this case I have create a very "bottleneck" function that does the distinct and it is still faster.

 public class Program
    {
      public static void Main(string[] arg)
        {
            //create the list
            List> listOfList = new List>()
                                      {
                                          new List()
                                              {
                                                  "1.1","2.2","1.1","1.1","2.2","1.1","1.1","2.2","1.1","1.1"
                                              }
                                      ,
                                       new List()
                                              {
                                                  "2.1","2.2","2.3","2.3","1.1","2.2","1.1","1.1","2.2","1.1","1.1","2.2","1.1","1.1","2.2","1.1","1.1","2.2","1.1"
                                              }
                                      };
            //stopwatch using Linq
            Stopwatch stopwatch = new Stopwatch();
            stopwatch.Start();

            int totalUsingLinq = listOfList.Sum(l => l.Distinct().Count());


            stopwatch.Stop();
            Console.WriteLine("Using Linq:{0}", stopwatch.Elapsed); //000012150    
            int totalUsingFor = 0;
            //stopwatch using classic for 
            stopwatch.Reset();
            stopwatch.Start();
            totalUsingFor = 0;
            for (int i = 0; i < listOfList.Count; i++)
            {
                var mainItem = listOfList[i];
                if (mainItem != null)
                {
                    for(int y=0;y list)
        {
            var item = list[index];
            for(int i=index+1;i