Dictionary Vs Hashtable Comparison In .NET

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Introduction

In .NET, Dictionary and Hashtable are two key-value pair types of data structures. They are similar but with some key differences. You may be wondering why there are two very similar data structures in C#. Well, Microsoft adds to the language but doesn't remove much from it. With that in mind, I'll be going over in detail the similarities and differences between the generic dictionary and hashtable.

Summary Table

Analysis TypeDictionaryHashtable
.NET Version >= 2.0 >= 1.1
PerformanceFastestFast
NamespaceSystem.Collections.GenericSystem.Collections
Element TypeKeyValuePairDictionaryEntry
GenericYesNo
Key ImmutableYesYes
Thread SafeNo | Multiple Readers OnlyNo | Multiple Readers and One Writer
Underlying Data StructureHashtableHashtable

.NET Version

Hashtable has been around a long time since the 1.1 version of .NET but Dictionary came in in 2.0 of .NET.

Performance

The most important consideration between Dictionary and Hashtable is how fast are they. The testing methods are as follows.

Below is a summary table of the results.

Performance Summary Table
MethodDictionary SpeedHashtable Speed
Add8003ms28178ms
Iterator662ms1725ms
Indexer5021ms9561ms
Update13673ms26548ms
Boxing and Unboxing

Before we get into testing these data structures we need to talk about boxing and unboxing. Since Hashtable uses boxing and unboxing to store and retrieve the items, it is a performance hit. Boxing is assigning a variable to a class of type object. So if I had an int equal to 3, I could assign it to a variable and type Object. See example.

int number = 3;//Starting number
Console.WriteLine("Starting value:" + number);//Print to screen
Object storedValue = number;//boxing, converting to type Object
int retievedValue = (int)storedValue;//unboxing, converting to original type
Console.WriteLine("Ending value:" + number);//Print to screen

It is this converting to an object and back again that is a concern for Hyashtable's performance. We'll do some testing to see how much this impacts performance and in which uses cases.

Type-Safe

The opposite of boxing and unboxing is the usage of type-safe methods and classes. It is an understanding the type is consistent and you can assume to be interacting with the same type and methods of that type. C# is a mostly type-safe language. A dictionary is a type-safe object that uses generics.

Add Speed Test

This will be a test to add a million objects to a Hashtable to see how it scales.

Test ParametersTotal
Tests10
Function Calls Per Test100
Objects Per Function Call1 million
Hashtable Add Test Method
void TestMethod(Dictionary<string, DateTime> dictionary, Hashtable destinationHashtable)
{
    foreach (KeyValuePair<string, DateTime> source in dictionary)
    {
        destinationHashtable.Add(source.Key, source.Value);//Add key and value to Hashtable
    }
}
Dictionary Add Test Method
void TestMethod(Dictionary<string, DateTime> dictionary, Dictionary<string, DateTime> destinationDictionary)
{
    foreach (KeyValuePair<string, DateTime> source in dictionary)
    {
        destinationDictionary.Add(source.Key, source.Value);//Add key and value to Dictionary
    }
}
Hashtable Add Code Output
Test 1:Function Calls:100, In 0m 27s 526ms
Test 2:Function Calls:100, In 0m 27s 510ms
Test 3:Function Calls:100, In 0m 27s 919ms
Test 4:Function Calls:100, In 0m 27s 560ms
Test 5:Function Calls:100, In 0m 28s 308ms
Test 6:Function Calls:100, In 0m 27s 984ms
Test 7:Function Calls:100, In 0m 27s 613ms
Test 8:Function Calls:100, In 0m 28s 64ms
Test 9:Function Calls:100, In 0m 29s 506ms
Test 10:Function Calls:100, In 0m 29s 786ms
Hashtable Add Method Average Speed:28178ms, In 10 Tests
Dictionary Add Code Output
Test 1:Function calls:100, In 0m 8s 116ms
Test 2:Function calls:100, In 0m 8s 263ms
Test 3:Function calls:100, In 0m 8s 24ms
Test 4:Function calls:100, In 0m 8s 348ms
Test 5:Function calls:100, In 0m 8s 117ms
Test 6:Function calls:100, In 0m 7s 931ms
Test 7:Function calls:100, In 0m 7s 758ms
Test 8:Function calls:100, In 0m 7s 870ms
Test 9:Function calls:100, In 0m 7s 889ms
Test 10:Function calls:100, In 0m 7s 711ms
Dictionary Add Method Average speed:8003ms, In 10 tests
Full Hashtable Add Test Code
using System.Collections;
using System.Diagnostics;
int numberOfTests = 10;//Number of tests 
int numberOfFunctionCalls = 100;//Number of function calls made per test
int numberOfObjectsToCreate = 1000000;//Number test objects
string testName = "Hashtable Add Method";//Test name to print to average

void TestMethod(Dictionary<string, DateTime> dictionary, Hashtable destinationHashtable)
{
    foreach (KeyValuePair<string, DateTime> source in dictionary)
    {
        destinationHashtable.Add(source.Key, source.Value);
    }
}

List<double> testSpeedList = new List<double>();
for (int testIndex = 0; testIndex < numberOfTests; testIndex++)
{
    testSpeedList.Add(StartTest(testIndex));
}
Console.WriteLine($"{testName} Average Speed:{Math.Round(testSpeedList.Average())}ms, In {numberOfTests} Tests");

double StartTest(int testIndex)
{
    Stopwatch stopwatch = new Stopwatch();
    Dictionary<string, DateTime> testData = GetDictionaryData();//Get intial random generated data
    for (int i = 0; i < numberOfFunctionCalls; i++)
    {
        Hashtable destinationHashtable = new Hashtable();
        stopwatch.Start();//Start the Stopwatch timer
        TestMethod(testData, destinationHashtable);//
        stopwatch.Stop();//Stop the Stopwatch timer
    }
    stopwatch.Stop();//Stop the Stopwatch timer
    Console.WriteLine($"Test {testIndex + 1}:Function Calls:{numberOfFunctionCalls}, In {stopwatch.Elapsed.Minutes}m {stopwatch.Elapsed.Seconds}s {stopwatch.Elapsed.Milliseconds}ms");
    return stopwatch.Elapsed.TotalMilliseconds;
}

Dictionary<string, DateTime> GetDictionaryData()
{
    Dictionary<string, DateTime> testData = new Dictionary<string, DateTime>();

    while (numberOfObjectsToCreate > testData.Count)
    {
        DateTime date = GetDateTime();
        string dateString = date.ToShortDateString();
        if (!testData.ContainsKey(dateString))
        {
            testData[dateString] = date;
        }
    }
    return testData;
}

int GetRandomInt(int minNumber, int maxNumber)
{
    Random random = new Random();//Create Random class
    int randomInt = random.Next(minNumber, maxNumber);//Get a random number between 1 and the maxnumber
    return randomInt;
}

DateTime GetDateTime()
{
    DateTime dateTime = new DateTime(GetRandomInt(1, 6000), GetRandomInt(1, 12), GetRandomInt(1, 29));
    return dateTime;
}
Full Dictionary Add Test Code
using System.Collections;
using System.Diagnostics;
int numberOfTests = 10;//Number of tests 
int numberOfFunctionCalls = 100;//Number of function calls made per test
int numberOfObjectsToCreate = 1000000;//Number test objects
string testName = "Dictionary Add Method";//Test name to print to average

void TestMethod(Dictionary<string, DateTime> dictionary, Dictionary<string, DateTime> destinationDictionary)
{
    foreach (KeyValuePair<string, DateTime> source in dictionary)
    {
        destinationDictionary.Add(source.Key, source.Value);
    }
}

List<double> testSpeedList = new List<double>();
for (int testIndex = 0; testIndex < numberOfTests; testIndex++)
{
    testSpeedList.Add(StartTest(testIndex));
}
Console.WriteLine($"{testName} Average speed:{Math.Round(testSpeedList.Average())}ms, In {numberOfTests} tests");

double StartTest(int testIndex)
{
    Stopwatch stopwatch = new Stopwatch();
    Dictionary<string, DateTime> testData = GetDictionaryData();//Get intial random generated data
    for (int i = 0; i < numberOfFunctionCalls; i++)
    {
        Dictionary<string, DateTime> destinationDictionary = new Dictionary<string, DateTime>();
        stopwatch.Start();//Start the Stopwatch timer
        TestMethod(testData, destinationDictionary);//
        stopwatch.Stop();//Stop the Stopwatch timer
    }
    stopwatch.Stop();//Stop the Stopwatch timer
    Console.WriteLine($"Test {testIndex + 1}:Function calls:{numberOfFunctionCalls}, In {stopwatch.Elapsed.Minutes}m {stopwatch.Elapsed.Seconds}s {stopwatch.Elapsed.Milliseconds}ms");
    return stopwatch.Elapsed.TotalMilliseconds;
}

Dictionary<string, DateTime> GetDictionaryData()
{
    Dictionary<string, DateTime> testData = new Dictionary<string, DateTime>();

    while (numberOfObjectsToCreate > testData.Count)
    {
        DateTime date = GetDateTime();
        string dateString = date.ToShortDateString();
        if (!testData.ContainsKey(dateString))
        {
            testData[dateString] = date;
        }
    }
    return testData;
}

int GetRandomInt(int minNumber, int maxNumber)
{
    Random random = new Random();//Create Random class
    int randomInt = random.Next(minNumber, maxNumber);//Get a random number between 1 and the maxnumber
    return randomInt;
}

DateTime GetDateTime()
{
    DateTime dateTime = new DateTime(GetRandomInt(1, 6000), GetRandomInt(1, 12), GetRandomInt(1, 29));
    return dateTime;
}
Hashtable Iterator Speed Test
Test Parameters
Test ParametersTotal
Tests10
Function Calls Per Test100
Objects Per Function Call1 million
Hashtable Iterator Speed Test Code
void TestMethod(Hashtable hashtable)
{
    foreach (DictionaryEntry dicEntry in hashtable)
    {
        //some logic
    }
}
Dictionary Iterator Speed Test Code
void TestMethod(Dictionary<string, DateTime> dictionary)
{
    foreach (KeyValuePair<string,DateTime> keyValuePair in dictionary)
    {
        //some logic
    }
}
Hashtable Iterator Code Output
Test 1:Function Calls:100, In 0m 1s 755ms
Test 2:Function Calls:100, In 0m 1s 700ms
Test 3:Function Calls:100, In 0m 1s 706ms
Test 4:Function Calls:100, In 0m 1s 719ms
Test 5:Function Calls:100, In 0m 1s 686ms
Test 6:Function Calls:100, In 0m 1s 724ms
Test 7:Function Calls:100, In 0m 1s 761ms
Test 8:Function Calls:100, In 0m 1s 745ms
Test 9:Function Calls:100, In 0m 1s 695ms
Test 10:Function Calls:100, In 0m 1s 756ms
Hashtable Iterator Average Speed:1725ms, In 10 Tests
Dictionary Iterator Code Output
Test 1:Function Calls:100, In 0m 0s 688ms
Test 2:Function Calls:100, In 0m 0s 659ms
Test 3:Function Calls:100, In 0m 0s 658ms
Test 4:Function Calls:100, In 0m 0s 658ms
Test 5:Function Calls:100, In 0m 0s 658ms
Test 6:Function Calls:100, In 0m 0s 659ms
Test 7:Function Calls:100, In 0m 0s 657ms
Test 8:Function Calls:100, In 0m 0s 657ms
Test 9:Function Calls:100, In 0m 0s 660ms
Test 10:Function Calls:100, In 0m 0s 664ms
Dictionary Iterator Average Speed:662ms, In 10 Tests
Full Hashtable Iterator Test Code
using System.Collections;
using System.Diagnostics;

int numberOfTests = 10;//Number of tests 
int numberOfFunctionCalls = 100;//Number of function calls made per test
int numberOfObjectsToCreate = 1000000;//Number test objects
string testName = "Hashtable Iterator";//Test name to print to average
void TestMethod(Hashtable hashtable)
{
    foreach (DictionaryEntry dicEntry in hashtable)
    {
        //some logic
    }
}
List<double> testSpeedList = new List<double>();
for (int testIndex = 0; testIndex < numberOfTests; testIndex++)
{
    testSpeedList.Add(StartTest(testIndex));
}
Console.WriteLine($"{testName} Average Speed:{Math.Round(testSpeedList.Average())}ms, In {numberOfTests} Tests");

double StartTest(int testIndex)
{
    Stopwatch stopwatch = new Stopwatch();
    Hashtable testData = GetHashtableData();//Get intial random generated data
    for (int i = 0; i < numberOfFunctionCalls; i++)
    {
        Hashtable destinationHashtable = new Hashtable();
        stopwatch.Start();//Start the Stopwatch timer
        TestMethod(testData);//
        stopwatch.Stop();//Stop the Stopwatch timer
    }
    stopwatch.Stop();//Stop the Stopwatch timer
    Console.WriteLine($"Test {testIndex + 1}:Function Calls:{numberOfFunctionCalls}, In {stopwatch.Elapsed.Minutes}m {stopwatch.Elapsed.Seconds}s {stopwatch.Elapsed.Milliseconds}ms");
    return stopwatch.Elapsed.TotalMilliseconds;
}

Hashtable GetHashtableData()
{
    Hashtable testData = new Hashtable();

    while (numberOfObjectsToCreate > testData.Count)
    {
        DateTime date = GetDateTime();
        string dateString = date.ToShortDateString();
        if (!testData.ContainsKey(dateString))
        {
            testData[dateString] = date;
        }
    }
    return testData;
}

int GetRandomInt(int minNumber, int maxNumber)
{
    Random random = new Random();//Create Random class
    int randomInt = random.Next(minNumber, maxNumber);//Get a random number between 1 and the maxnumber
    return randomInt;
}

DateTime GetDateTime()
{
    DateTime dateTime = new DateTime(GetRandomInt(1, 6000), GetRandomInt(1, 12), GetRandomInt(1, 29));
    return dateTime;
}
Full Dictionary Iterator Test Code
using System.Collections;
using System.Diagnostics;

int numberOfTests = 10;//Number of tests 
int numberOfFunctionCalls = 100;//Number of function calls made per test
int numberOfObjectsToCreate = 1000000;//Number test objects
string testName = "Dictionary Iterator";//Test name to print to average
void TestMethod(Dictionary<string, DateTime> dictionary)
{
    foreach (KeyValuePair<string,DateTime> keyValuePair in dictionary)
    {
        //some logic
    }
}


List<double> testSpeedList = new List<double>();
for (int testIndex = 0; testIndex < numberOfTests; testIndex++)
{
    testSpeedList.Add(StartTest(testIndex));
}
Console.WriteLine($"{testName} Average Speed:{Math.Round(testSpeedList.Average())}ms, In {numberOfTests} Tests");

double StartTest(int testIndex)
{
    Stopwatch stopwatch = new Stopwatch();
    Dictionary<string,DateTime> testData = GetDictionaryData();//Get intial random generated data
    for (int i = 0; i < numberOfFunctionCalls; i++)
    {
        stopwatch.Start();//Start the Stopwatch timer
        TestMethod(testData);//
        stopwatch.Stop();//Stop the Stopwatch timer
    }
    stopwatch.Stop();//Stop the Stopwatch timer
    Console.WriteLine($"Test {testIndex + 1}:Function Calls:{numberOfFunctionCalls}, In {stopwatch.Elapsed.Minutes}m {stopwatch.Elapsed.Seconds}s {stopwatch.Elapsed.Milliseconds}ms");
    return stopwatch.Elapsed.TotalMilliseconds;
}

Dictionary<string, DateTime> GetDictionaryData()
{
    Dictionary<string, DateTime> testData = new Dictionary<string, DateTime>();

    while (numberOfObjectsToCreate > testData.Count)
    {
        DateTime date = GetDateTime();
        string dateString = date.ToShortDateString();
        if (!testData.ContainsKey(dateString))
        {
            testData[dateString] = date;
        }
    }
    return testData;
}

int GetRandomInt(int minNumber, int maxNumber)
{
    Random random = new Random();//Create Random class
    int randomInt = random.Next(minNumber, maxNumber);//Get a random number between 1 and the maxnumber
    return randomInt;
}

DateTime GetDateTime()
{
    DateTime dateTime = new DateTime(GetRandomInt(1, 6000), GetRandomInt(1, 12), GetRandomInt(1, 29));
    return dateTime;
}
Indexer Speed Test
Test Parameters
Test ParametersTotal
Tests10
Function Calls Per Test100
Objects Per Function Call1 million
Hashtable Indexer Speed Test Code
void TestMethod(Hashtable hashtable)
{
    foreach (string key in keysList)
    {
        DateTime dateTime = ((DateTime)hashtable[key]).AddHours(1);//Get data through the Indexer
        double ticks = dateTime.Ticks;
    }
}
Dictionary Indexer Speed Test Code
void TestMethod(Dictionary<string,DateTime> dictionary)
{
    foreach (string key in keysList)
    {
        DateTime dateTime = dictionary[key].AddHours(1);//Get data through the Indexer
        double ticks = dateTime.Ticks;
    }
}
Hashtable Indexer Code Output
Test 1:Function Calls:100, In 0m 10s 40ms
Test 2:Function Calls:100, In 0m 9s 428ms
Test 3:Function Calls:100, In 0m 9s 273ms
Test 4:Function Calls:100, In 0m 9s 467ms
Test 5:Function Calls:100, In 0m 9s 510ms
Test 6:Function Calls:100, In 0m 9s 503ms
Test 7:Function Calls:100, In 0m 9s 553ms
Test 8:Function Calls:100, In 0m 9s 500ms
Test 9:Function Calls:100, In 0m 9s 646ms
Test 10:Function Calls:100, In 0m 9s 682ms
Hashtable Indexer Average Speed:9561ms, In 10 Tests
Dictionary Indexer Code Output
Test 1:Function Calls:100, In 0m 4s 997ms
Test 2:Function Calls:100, In 0m 4s 780ms
Test 3:Function Calls:100, In 0m 4s 957ms
Test 4:Function Calls:100, In 0m 4s 997ms
Test 5:Function Calls:100, In 0m 4s 866ms
Test 6:Function Calls:100, In 0m 4s 960ms
Test 7:Function Calls:100, In 0m 5s 342ms
Test 8:Function Calls:100, In 0m 5s 754ms
Test 9:Function Calls:100, In 0m 4s 804ms
Test 10:Function Calls:100, In 0m 4s 752ms
Dictionary Indexer Average Speed:5021ms, In 10 Tests
Full Hashtable Indexer Test Code
using System.Collections;
using System.Diagnostics;

int numberOfTests = 10;//Number of tests 
int numberOfFunctionCalls = 100;//Number of function calls made per test
int numberOfObjectsToCreate = 1000000;//Number test objects
string testName = "Hashtable Indexer";//Test name to print to average
List<string> keysList = new List<string>();
void TestMethod(Hashtable hashtable)
{
    foreach (string key in keysList)
    {
        DateTime dateTime = ((DateTime)hashtable[key]).AddHours(1);//Get data through the Indexer
        double ticks = dateTime.Ticks;
    }
}

List<double> testSpeedList = new List<double>();
for (int testIndex = 0; testIndex < numberOfTests; testIndex++)
{
    testSpeedList.Add(StartTest(testIndex));
}
Console.WriteLine($"{testName} Average Speed:{Math.Round(testSpeedList.Average())}ms, In {numberOfTests} Tests");

double StartTest(int testIndex)
{
    Stopwatch stopwatch = new Stopwatch();
    Hashtable testData = GetHashtableData();//Get intial random generated data
    for (int i = 0; i < numberOfFunctionCalls; i++)
    {
        stopwatch.Start();//Start the Stopwatch timer
        TestMethod(testData);//
        stopwatch.Stop();//Stop the Stopwatch timer
    }
    stopwatch.Stop();//Stop the Stopwatch timer
    Console.WriteLine($"Test {testIndex + 1}:Function Calls:{numberOfFunctionCalls}, In {stopwatch.Elapsed.Minutes}m {stopwatch.Elapsed.Seconds}s {stopwatch.Elapsed.Milliseconds}ms");
    return stopwatch.Elapsed.TotalMilliseconds;
}

Hashtable GetHashtableData()
{
    Hashtable testData = new Hashtable();
    keysList = new List<string>();
    while (numberOfObjectsToCreate > testData.Count)
    {
        DateTime date = GetDateTime();
        string dateString = date.ToShortDateString();
        if (!testData.ContainsKey(dateString))
        {
            testData[dateString] = date;
            keysList.Add(dateString);
        }
    }
    return testData;
}

int GetRandomInt(int minNumber, int maxNumber)
{
    Random random = new Random();//Create Random class
    int randomInt = random.Next(minNumber, maxNumber);//Get a random number between 1 and the maxnumber
    return randomInt;
}

DateTime GetDateTime()
{
    DateTime dateTime = new DateTime(GetRandomInt(1, 6000), GetRandomInt(1, 12), GetRandomInt(1, 29));
    return dateTime;
}
Full Dictionary Indexer Test Code
using System.Diagnostics;

int numberOfTests = 10;//Number of tests 
int numberOfFunctionCalls = 100;//Number of function calls made per test
int numberOfObjectsToCreate = 1000000;//Number test objects
string testName = "Dictionary Indexer";//Test name to print to average
List<string> keysList = new List<string>();
void TestMethod(Dictionary<string,DateTime> dictionary)
{
    foreach (string key in keysList)
    {
        DateTime dateTime = dictionary[key].AddHours(1);//Get data through the Indexer
        double ticks = dateTime.Ticks;
    }
}
List<double> testSpeedList = new List<double>();
for (int testIndex = 0; testIndex < numberOfTests; testIndex++)
{
    testSpeedList.Add(StartTest(testIndex));
}
Console.WriteLine($"{testName} Average Speed:{Math.Round(testSpeedList.Average())}ms, In {numberOfTests} Tests");

double StartTest(int testIndex)
{
    Stopwatch stopwatch = new Stopwatch();
    Dictionary<string,DateTime> testData = GetDictionaryData();//Get intial random generated data
    for (int i = 0; i < numberOfFunctionCalls; i++)
    {
        stopwatch.Start();//Start the Stopwatch timer
        TestMethod(testData);//
        stopwatch.Stop();//Stop the Stopwatch timer
    }
    stopwatch.Stop();//Stop the Stopwatch timer
    Console.WriteLine($"Test {testIndex + 1}:Function Calls:{numberOfFunctionCalls}, In {stopwatch.Elapsed.Minutes}m {stopwatch.Elapsed.Seconds}s {stopwatch.Elapsed.Milliseconds}ms");
    return stopwatch.Elapsed.TotalMilliseconds;
}

Dictionary<string, DateTime> GetDictionaryData()
{
    Dictionary<string, DateTime> testData = new Dictionary<string, DateTime>();
    keysList = new List<string>();
    while (numberOfObjectsToCreate > testData.Count)
    {
        DateTime date = GetDateTime();
        string dateString = date.ToShortDateString();
        if (!testData.ContainsKey(dateString))
        {
            testData[dateString] = date;
            keysList.Add(dateString);
        }
    }
    return testData;
}

int GetRandomInt(int minNumber, int maxNumber)
{
    Random random = new Random();//Create Random class
    int randomInt = random.Next(minNumber, maxNumber);//Get a random number between 1 and the maxnumber
    return randomInt;
}

DateTime GetDateTime()
{
    DateTime dateTime = new DateTime(GetRandomInt(1, 6000), GetRandomInt(1, 12), GetRandomInt(1, 29));
    return dateTime;
}
Update Speed Test
Test Parameters
Test ParametersTotal
Tests10
Function Calls Per Test100
Objects Per Function Call1 million
Hashtable Update Speed Test Code
void TestMethod(Hashtable hashtable)
{
    foreach (string key in keysList)
    {
        hashtable[key] = DateTime.Now;
    }
}
Dictionary Update Speed Test Code
void TestMethod(Dictionary<string, DateTime> dictionary)
{
    foreach (string key in keysList)
    {
        dictionary[key] = DateTime.Now;
    }
}
Hashtable Update Code Output
Test 1:Function Calls:100, In 0m 26s 619ms
Test 2:Function Calls:100, In 0m 27s 341ms
Test 3:Function Calls:100, In 0m 27s 156ms
Test 4:Function Calls:100, In 0m 26s 735ms
Test 5:Function Calls:100, In 0m 26s 582ms
Test 6:Function Calls:100, In 0m 26s 706ms
Test 7:Function Calls:100, In 0m 24s 860ms
Test 8:Function Calls:100, In 0m 26s 759ms
Test 9:Function Calls:100, In 0m 26s 276ms
Test 10:Function Calls:100, In 0m 26s 438ms
Hashtable Update Average Speed:26548ms, In 10 Tests
Dictionary Update Code Output
Test 1:Function Calls:100, In 0m 13s 805ms
Test 2:Function Calls:100, In 0m 13s 644ms
Test 3:Function Calls:100, In 0m 13s 879ms
Test 4:Function Calls:100, In 0m 13s 697ms
Test 5:Function Calls:100, In 0m 13s 900ms
Test 6:Function Calls:100, In 0m 13s 373ms
Test 7:Function Calls:100, In 0m 13s 706ms
Test 8:Function Calls:100, In 0m 13s 246ms
Test 9:Function Calls:100, In 0m 14s 94ms
Test 10:Function Calls:100, In 0m 13s 381ms
Dictionary Update Average Speed:13673ms, In 10 Tests
Full Hashtable Update Test Code
using System.Collections;
using System.Diagnostics;

int numberOfTests = 10;//Number of tests 
int numberOfFunctionCalls = 100;//Number of function calls made per test
int numberOfObjectsToCreate = 1000000;//Number test objects
string testName = "Hashtable Update";//Test name to print to average
List<string> keysList = new List<string>();
void TestMethod(Hashtable hashtable)
{
    foreach (string key in keysList)
    {
        hashtable[key] = DateTime.Now;
    }
}

List<double> testSpeedList = new List<double>();
for (int testIndex = 0; testIndex < numberOfTests; testIndex++)
{
    testSpeedList.Add(StartTest(testIndex));
}
Console.WriteLine($"{testName} Average Speed:{Math.Round(testSpeedList.Average())}ms, In {numberOfTests} Tests");

double StartTest(int testIndex)
{
    Stopwatch stopwatch = new Stopwatch();
    Hashtable testData = GetHashtableData();//Get intial random generated data
    for (int i = 0; i < numberOfFunctionCalls; i++)
    {
        stopwatch.Start();//Start the Stopwatch timer
        TestMethod(testData);//
        stopwatch.Stop();//Stop the Stopwatch timer
    }
    stopwatch.Stop();//Stop the Stopwatch timer
    Console.WriteLine($"Test {testIndex + 1}:Function Calls:{numberOfFunctionCalls}, In {stopwatch.Elapsed.Minutes}m {stopwatch.Elapsed.Seconds}s {stopwatch.Elapsed.Milliseconds}ms");
    return stopwatch.Elapsed.TotalMilliseconds;
}

Hashtable GetHashtableData()
{
    Hashtable testData = new Hashtable();
    keysList = new List<string>();
    while (numberOfObjectsToCreate > testData.Count)
    {
        DateTime date = GetDateTime();
        string dateString = date.ToShortDateString();
        if (!testData.ContainsKey(dateString))
        {
            testData[dateString] = date;
            keysList.Add(dateString);
        }
    }
    return testData;
}

int GetRandomInt(int minNumber, int maxNumber)
{
    Random random = new Random();//Create Random class
    int randomInt = random.Next(minNumber, maxNumber);//Get a random number between 1 and the maxnumber
    return randomInt;
}

DateTime GetDateTime()
{
    DateTime dateTime = new DateTime(GetRandomInt(1, 6000), GetRandomInt(1, 12), GetRandomInt(1, 29));
    return dateTime;
}
Full Dictionary Update Test Code

using System.Diagnostics;

int numberOfTests = 10;//Number of tests 
int numberOfFunctionCalls = 100;//Number of function calls made per test
int numberOfObjectsToCreate = 1000000;//Number test objects
string testName = "Dictionary Update";//Test name to print to average
List<string> keysList = new List<string>();
void TestMethod(Dictionary<string, DateTime> dictionary)
{
    foreach (string key in keysList)
    {
        dictionary[key] = DateTime.Now;
    }
}

List<double> testSpeedList = new List<double>();
for (int testIndex = 0; testIndex < numberOfTests; testIndex++)
{
    testSpeedList.Add(StartTest(testIndex));
}
Console.WriteLine($"{testName} Average Speed:{Math.Round(testSpeedList.Average())}ms, In {numberOfTests} Tests");

double StartTest(int testIndex)
{
    Stopwatch stopwatch = new Stopwatch();
    Dictionary<string, DateTime> testData = GetDictionaryData();//Get intial random generated data
    for (int i = 0; i < numberOfFunctionCalls; i++)
    {
        stopwatch.Start();//Start the Stopwatch timer
        TestMethod(testData);//
        stopwatch.Stop();//Stop the Stopwatch timer
    }
    stopwatch.Stop();//Stop the Stopwatch timer
    Console.WriteLine($"Test {testIndex + 1}:Function Calls:{numberOfFunctionCalls}, In {stopwatch.Elapsed.Minutes}m {stopwatch.Elapsed.Seconds}s {stopwatch.Elapsed.Milliseconds}ms");
    return stopwatch.Elapsed.TotalMilliseconds;
}

Dictionary<string, DateTime> GetDictionaryData()
{
    Dictionary<string, DateTime> testData = new Dictionary<string, DateTime>();
    keysList = new List<string>();
    while (numberOfObjectsToCreate > testData.Count)
    {
        DateTime date = GetDateTime();
        string dateString = date.ToShortDateString();
        if (!testData.ContainsKey(dateString))
        {
            testData[dateString] = date;
            keysList.Add(dateString);
        }
    }
    return testData;
}

int GetRandomInt(int minNumber, int maxNumber)
{
    Random random = new Random();//Create Random class
    int randomInt = random.Next(minNumber, maxNumber);//Get a random number between 1 and the maxnumber
    return randomInt;
}

DateTime GetDateTime()
{
    DateTime dateTime = new DateTime(GetRandomInt(1, 6000), GetRandomInt(1, 12), GetRandomInt(1, 29));
    return dateTime;
}

Namespace

Both dictionaries and hashtables reside in the System.Collections namespace. The dictionary is found in a subsection of System.Collection.Generic. It is aptly named as it uses generics to set the type of the key-value pairs at run time.

Element Type

Hashtable uses the DictionaryEntry for the key and value properties while the Dictionary uses the KeyValuePair generics that have key and value properties. So they both have key and value properties just the class is different.

Generic

The dictionary uses generics which means that type for the key and values are known at compile time. This makes it faster and less error-prone than the box and unboxing way that Hashtable uses. It seems like not using generics makes things more generalized but there is a performance paid.

Key Immutable

This is important for the consistency of the data structure. Both Dictionary and Hashtable require this other wise they might become unstable.

Thread Safe

Both allow multiple readers, which makes that there can be multiple threads reading the Dictionary or HashTable. The dictionary is not considered thread-safe. But does it need to be when there is a Concurrent Dictionary collection type that is thread-safe? The interesting thing is that Hashtable does allow for one thread to write to the hashtable but it can't happen while another thread is looping through the dictionary. Some may consider hashtables to be thread-safe and a good reason to use a hashtable. I do not because if there's a change in the hashtable while another reader thread is looping through the hashtable then an exception will occur. This is not thread-safe.

Conclusion

What should you use Hashtable or Dictionary? You should use Dictionary, it has significant performance improvements that I have tested throughout this article. All of my tests show that Dictionary had almost twice as much speed improvement over the hashtable. It shows as the data grows larger. The other thing is that Microsoft says not to use a nongeneric collection which the hashtable is. This is because of the performance issue but also because they are error-prone. Do you know any interesting facts about Dictionary or Hashtable that I missed? Let me know in the comments below.

Do you know any interesting facts about Dictionary or Hashtable that I missed? Let me know in the comments below.

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