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Hashtable Constructor (IDictionary, Single)


Initializes a new instance of the Hashtable class by copying the elements from the specified dictionary to the new Hashtable object. The new Hashtable object has an initial capacity equal to the number of elements copied, and uses the specified load factor, and the default hash code provider and comparer.

Namespace:   System.Collections
Assembly:  mscorlib (in mscorlib.dll)

public Hashtable(
	IDictionary d,
	float loadFactor


Type: System.Collections.IDictionary

The IDictionary object to copy to a new Hashtable object.

Type: System.Single

A number in the range from 0.1 through 1.0 that is multiplied by the default value which provides the best performance. The result is the maximum ratio of elements to buckets.

Exception Condition

d is null.


loadFactor is less than 0.1.


loadFactor is greater than 1.0.

The initial capacity is set to the number of elements in the source dictionary. Capacity is automatically increased as required based on the load factor.

The load factor is the maximum ratio of elements to buckets. A smaller load factor means faster lookup at the cost of increased memory consumption. A load factor of 1.0 is the best balance between speed and size.

When the actual load factor reaches the specified load factor, the number of buckets is automatically increased to the smallest prime number that is larger than twice the current number of buckets.

The hash code provider dispenses hash codes for keys in the Hashtable object. The default hash code provider is the key's implementation of Object.GetHashCode.

The comparer determines whether two keys are equal. Every key in a Hashtable must be unique. The default comparer is the key's implementation of Object.Equals.

The elements of the new Hashtable are sorted in the same order in which the enumerator iterates through the IDictionary object.

This constructor is an O(n) operation, where n is the number of elements in the d parameter.

The following code example creates hash tables using different Hashtable constructors and demonstrates the differences in the behavior of the hash tables, even if each one contains the same elements.

using System;
using System.Collections;
using System.Globalization;

class myCultureComparer : IEqualityComparer
    public CaseInsensitiveComparer myComparer;

    public myCultureComparer()
        myComparer = CaseInsensitiveComparer.DefaultInvariant;

    public myCultureComparer(CultureInfo myCulture)
        myComparer = new CaseInsensitiveComparer(myCulture);

    public new bool Equals(object x, object y)
        if (myComparer.Compare(x, y) == 0)
            return true;
            return false;

    public int GetHashCode(object obj)
        // Compare the hash code for the lowercase versions of the strings.
        return obj.ToString().ToLower().GetHashCode();

public class SamplesHashtable

    public static void Main()

        // Create the dictionary.
        SortedList mySL = new SortedList();
        mySL.Add("FIRST", "Hello");
        mySL.Add("SECOND", "World");
        mySL.Add("THIRD", "!");

        // Create a hash table using the default comparer.
        Hashtable myHT1 = new Hashtable(mySL, (float).8);

        // Create a hash table using the specified IEqualityComparer that uses
        // the CaseInsensitiveComparer.DefaultInvariant to determine equality.
        Hashtable myHT2 = new Hashtable(mySL, (float).8, 
            new myCultureComparer());

        // Create a hash table using an IEqualityComparer that is based on
        // the Turkish culture (tr-TR) where "I" is not the uppercase
        // version of "i".
        CultureInfo myCul = new CultureInfo("tr-TR");
        Hashtable myHT3 = new Hashtable(mySL, (float).8, 
            new myCultureComparer(myCul));

        // Search for a key in each hash table.
        Console.WriteLine("first is in myHT1: {0}", myHT1.ContainsKey("first"));
        Console.WriteLine("first is in myHT2: {0}", myHT2.ContainsKey("first"));
        Console.WriteLine("first is in myHT3: {0}", myHT3.ContainsKey("first"));



This code produces the following output.
Results vary depending on the system's culture settings.

first is in myHT1: False
first is in myHT2: True
first is in myHT3: False


Universal Windows Platform
Available since 10
.NET Framework
Available since 1.1
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