String.Join(Of T) Method (String, IEnumerable(Of T))


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Concatenates the members of a collection, using the specified separator between each member.

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

Public Shared Function Join(Of T) (
	separator As String,
	values As IEnumerable(Of T)
) As String


Type: System.String

The string to use as a separator.separator is included in the returned string only if values has more than one element.

Type: System.Collections.Generic.IEnumerable(Of T)

A collection that contains the objects to concatenate.

Return Value

Type: System.String

A string that consists of the members of values delimited by the separator string. If values has no members, the method returns String.Empty.

Type Parameters


The type of the members of values.

Exception Condition

values is null.

If separator is null, an empty string (String.Empty) is used instead. If any member of values is null, an empty string is used instead.

Join(Of T)(String, IEnumerable(Of T)) is a convenience method that lets you concatenate each member of an IEnumerable(Of T) collection without first converting them to strings. The string representation of each object in the IEnumerable(Of T) collection is derived by calling that object's ToString method.

This method is particular useful with Language-Integrated Query (LINQ) query expressions. For example, the following code defines a very simple Animal class that contains the name of an animal and the order to which it belongs. It then defines a List(Of T) object that contains a number of Animal objects. The Enumerable.Where(Of TSource) extension method is called to extract the Animal objects whose Order property equals "Rodent". The result is passed to the Join(Of T)(String, IEnumerable(Of T)) method.

Imports System.Collections.Generic

Public Class Animal
   Public Kind As String
   Public Order As String

   Public Sub New(kind As String, order As String)
      Me.Kind = kind
      Me.Order = order
   End Sub

   Public Overrides Function ToString() As String
      Return Me.Kind
   End Function
End Class

Module Example
   Public Sub Main()
      Dim animals As New List(Of Animal)
      animals.Add(New Animal("Squirrel", "Rodent"))
      animals.Add(New Animal("Gray Wolf", "Carnivora"))
      animals.Add(New Animal("Capybara", "Rodent")) 
      Dim output As String = String.Join(" ", animals.Where(Function(animal) _
                                           animal.Order = "Rodent"))
   End Sub
End Module
' The example displays the following output:
'      Squirrel Capybara

The following example uses the Sieve of Eratosthenes algorithm to calculate the prime numbers that are less than or equal to 100. It assigns the result to a List(Of T) object of type integer, which it then passes to the Join(Of T)(String, IEnumerable(Of T)) method.

Imports System.Collections.Generic

Module Example
   Public Sub Main()
      Dim maxPrime As Integer = 100
      Dim primes As List(Of Integer) = GetPrimes(maxPrime)
      Console.WriteLine("Primes less than {0}:", maxPrime)
      Console.WriteLine("   {0}", String.Join(" ", primes))
   End Sub

   Private Function GetPrimes(maxPrime As Integer) As List(Of Integer)
      Dim values As Array = Array.CreateInstance(GetType(Integer), _
                              New Integer() { maxPrime - 1}, New Integer(){ 2 }) 
        ' Use Sieve of Eratosthenes to determine prime numbers.
      For ctr As Integer = values.GetLowerBound(0) To _
         If CInt(values.GetValue(ctr)) = 1 Then Continue For

         For multiplier As Integer = ctr To maxPrime \ 2
            If ctr * multiplier <= maxPrime Then values.SetValue(1, ctr * multiplier)

      Dim primes As New System.Collections.Generic.List(Of Integer)
      For ctr As Integer = values.GetLowerBound(0) To values.GetUpperBound(0)
         If CInt(values.GetValue(ctr)) = 0 Then primes.Add(ctr)
      Return primes
   End Function   
End Module
' The example displays the following output:
'    Primes less than 100:
'       2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97

Universal Windows Platform
Available since 8
.NET Framework
Available since 4.0
Portable Class Library
Supported in: portable .NET platforms
Available since 4.0
Windows Phone Silverlight
Available since 7.1
Windows Phone
Available since 8.1
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