VB.Net Tutorial/Collections/Hashtable

Add value pair to Hashtable and get value back by key

Imports System
Imports System.Collections
Class Test
  Shared Sub Main()
    Dim myTable As New Hashtable()
    myTable.Item("A") = 1
    myTable.Item("B") = 44
    myTable.Item("C") = 43
    myTable.Item("D") = 33
    myTable.Item("E") = 39
    Dim Country As String = "C"
    Dim Code As Integer = myTable.Item(Country)
    Console.WriteLine(Code)
  End Sub
End Class

43

ContainsKey

Imports System.Collections
public class Test
   public Shared Sub Main
        Dim myTable As New Hashtable
        Dim objKey As Object
        Dim objValue As Object
        "Populate the hash table.
        myTable.Add("H", 1)
        myTable.Add("L", 2)
        "Check before inserting another value.
        If Not myTable.ContainsKey("A") Then
            myTable.Add("A", 78)
        End If
        "Remove a value.
        myTable.Remove("L")
        "Display the hash table values.
        Console.WriteLine("The hash table contains " & myTable.Count & " elements.")
        For Each objKey In myTable.Keys
            objValue = myTable.Item(objKey)
            Console.WriteLine("ELEMENT KEY: " & objKey.ToString & vbCrLf & _
                   "ELEMENT VALUE: " & objValue.ToString)
        Next objKey

   End Sub
End class

The hash table contains 2 elements.
ELEMENT KEY: A
ELEMENT VALUE: 78
ELEMENT KEY: H
ELEMENT VALUE: 1

Find value and key in a Hashtable

Imports System.Collections
Public Module Hasher
    Dim Tablet As Hashtable = New Hashtable()
    Sub Main()
        AddToTable()
        FindItem("AAA")
        FindKey("BBB")
    End Sub
    Public Sub AddToTable()
        Tablet.Add("333", "WWWW")
        Tablet.Add("444", "AAA")
        Tablet.Add("BBB", "I386")
    End Sub
    Public Sub FindItem(ByVal item As String)
        If Tablet.ContainsValue(item) Then
            Console.WriteLine("Found {0} in the hashtable.", item)
        End If
    End Sub
    Public Sub FindKey(ByVal key As String)
        If Tablet.ContainsKey(key) Then
            Console.WriteLine("Found {0} in the list.", key)
        End If
    End Sub
End Module

Found AAA in the hashtable.
Found BBB in the list.

Get Enumerator from Hashtable

Imports System.Collections
public class Test
   public Shared Sub Main
        Dim Hash As New Hashtable()
        Hash.Add("5", "A")
        Hash.Add("6", "B")
        Hash.Add("7", "C")
    
        Dim Enumerator As IDictionaryEnumerator = Hash.GetEnumerator
    
        While (Enumerator.MoveNext())
          Console.WriteLine(Enumerator.Key.ToString + "=" + Enumerator.Value.ToString)
        End While

   End Sub
End class

5=A
6=B
7=C

Retrieve all keys, sort and iterate

Option Strict On
Imports System.Collections
Public Module modMain
   Public Sub Main()
      Dim airports As New Hashtable
      airports.Add("S", "SSS")
      airports.Add("X", "XXX")
      airports.Add("D", "DDD")
      airports.Add("R", "RRR")
      
      Dim keys As ICollection = airports.Keys
      Dim keysArray(airports.Count - 1) As String
      keys.CopyTo(keysArray, 0)
      Array.Sort(keysArray)
      For Each key As String in KeysArray
         Console.WriteLine("{0} is {1}", key, airports(key))
      Next
   End Sub
End Module

D is DDD
R is RRR
S is SSS
X is XXX

Retrieve all values, sort and iterate

Option Strict On
Imports System.Collections
Public Module modMain
   Public Sub Main()
      Dim airports As New Hashtable
      airports.Add("S", "SSS")
      airports.Add("X", "XXX")
      airports.Add("D", "DDD")
      airports.Add("R", "RRR")
      
      Dim values As ICollection = airports.Values
      Dim valuesArray(airports.Count - 1) As String
      values.CopyTo(valuesArray, 0)
      Array.Sort(valuesArray)
      Console.WriteLine()
      For Each value As String in valuesArray
         Console.WriteLine(value)
      Next
   End Sub
End Module

DDD
RRR
SSS
XXX

Retrieve single value from Hashtable by key

Option Strict On
Imports System.Collections
Public Module modMain
   Public Sub Main()
      Dim airports As New Hashtable
      airports.Add("JFK", "John F. Kennedy, New York")
      airports.Add("LAX", "Los Angeles International, Los Angeles")
      airports.Add("ORD", "O"Hare International, Chicago")
      airports.Add("LHR", "Heathrow Airport, London")
      Console.WriteLine(airports.Item("JFK"))
   End Sub
End Module

John F. Kennedy, New York

Use For Each to loop through all keys in Hashtable

Imports System.Collections
public class Test
   public Shared Sub Main
        Dim myTable As New Hashtable
        Dim objKey As Object
        Dim objValue As Object
        "Populate the hash table.
        myTable.Add("H", 1)
        myTable.Add("L", 2)
        "Check before inserting another value.
        If Not myTable.ContainsKey("A") Then
            myTable.Add("A", 78)
        End If
        "Remove a value.
        myTable.Remove("L")
        "Display the hash table values.
        Console.WriteLine("The hash table contains " & myTable.Count & " elements.")
        For Each objKey In myTable.Keys
            objValue = myTable.Item(objKey)
            Console.WriteLine("ELEMENT KEY: " & objKey.ToString & vbCrLf & _
                   "ELEMENT VALUE: " & objValue.ToString)
        Next objKey

   End Sub
End class

The hash table contains 2 elements.
ELEMENT KEY: A
ELEMENT VALUE: 78
ELEMENT KEY: H
ELEMENT VALUE: 1