Dictionary VS Hash Table

8. January 2008
Comments (3)

We all know how useful a hash table can be, but if you are using the .NET Framework 2.0 you should be using a Dictionary instead. A dictionary and a hash table in .NET 2.0 are very similar but with 1 main difference, a dictionary is faster because it does not need to box and unbox the data as a hash table would.

 

I made a simple program to see just how much faster a dictionary is than a hash table. I ran the test 20 times for each data set and the results were close each time. A GUID as the key and a boolean as the data.

This is the results of the last test for each dataset.

Time in Milliseconds for 100,000 keys Dictionary Hash Table
Inserting 34.41264 76.0970
Reading 18.9005 31.1648
Deleting 21.2474 30.4655

 

Time in Seconds for 10,000,000 keys Dictionary Hash Table
Inserting 6.5704143 26.9096540
Reading 3.1362891 5.6670613
Deleting 3.4623316 4.8830676

 

My comp specs

Vista Business 32bit, AMD 64 x2 5000+, 2GB ram

 

and now for the code I used. You can also download the project.  

 

 

 

 

using System;
using System.Collections;
using System.Collections.Generic;
using System.Diagnostics;
 
namespace hashVsDictionary
{
    internal class Program
    {
        private static void Main(string[] args)
        {
            #region init
 
            int num = 10000000;
            Guid[] guids = new Guid[num];
 
            Stopwatch s = new Stopwatch();
            s.Start();
 
            for (int i = 0; i < num; i++)
            {
                guids[i] = Guid.NewGuid();
            }
 
            s.Stop();
            Console.WriteLine("Data Creation = " + s.Elapsed);
            s.Reset();
 
            #endregion
 
            #region hash
 
            Hashtable hash = new Hashtable();
            s.Start();
            for (int i = 0; i < num; i++)
            {
                hash.Add(guids[i], true);
            }
            s.Stop();
            Console.WriteLine("Insert Hash = " + s.Elapsed);
            s.Reset();
 
            s.Start();
            for (int i = 0; i < num; i++)
            {
                bool b = Convert.ToBoolean(hash[guids[i]]);
            }
            Console.WriteLine("Extracting Hash = " + s.Elapsed);
            s.Reset();
 
            s.Start();
            for (int i = 0; i < num; i++)
            {
                hash.Remove(guids[i]);
            }
 
            Console.WriteLine("Removing Hash = " + s.Elapsed);
            s.Reset();
 
            #endregion
 
            #region dict
 
            Dictionary<Guid, bool> dict = new Dictionary<Guid, bool>();
            s.Start();
            for (int i = 0; i < num; i++)
            {
                dict.Add(guids[i], true);
            }
            s.Stop();
            Console.WriteLine("Insert Dictionary = " + s.Elapsed);
            s.Reset();
 
            s.Start();
            for (int i = 0; i < num; i++)
            {
                bool b = dict[guids[i]];
            }
            Console.WriteLine("Extracting Dict = " + s.Elapsed);
            s.Reset();
 
            s.Start();
            for (int i = 0; i < num; i++)
            {
                dict.Remove(guids[i]);
            }
            Console.WriteLine("Removing Dict = " + s.Elapsed);
            s.Reset();
 
            #endregion
 
            Console.ReadLine();
        }
    }
}

ASP.NET, Generics ,

Comments

Jeremy
Jeremy
2/27/2008 3:02:09 AM #
Great, Thank you for sharing this.  I've assumed dictionaries would be more efficient but have been looking for proof.  Thanks again!
Hmmm
Hmmm
5/19/2008 5:33:36 PM #
It's faster because Dictionary knows what to store.
But if you use to store Object, hashtable is way more faster.
From microsoft:
"The Dictionary class has the same functionality as the Hashtable class. A Dictionary of a specific type (other than Object) has better performance than a Hashtable for value types because the elements of Hashtable are of type Object and, therefore, boxing and unboxing typically occur if storing or retrieving a value type."
saty
saty
3/9/2010 4:15:41 PM #
HashTable accept null values for both Key and Value parameters. With Dictionary<TKey, TValue> this is not possible.
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