String.Join<T> Method (String, IEnumerable<T>)
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Updated: January 2011
Concatenates the members of a string collection, using the specified separator between each member.
Namespace: System
Assembly: mscorlib (in mscorlib.dll)
Syntax
'Declaration
<ComVisibleAttribute(False)> _
Public Shared Function Join(Of T) ( _
separator As String, _
values As IEnumerable(Of T) _
) As String
[ComVisibleAttribute(false)]
public static string Join<T>(
string separator,
IEnumerable<T> values
)
Type Parameters
- T
The type of the members of values.
Parameters
- separator
Type: System.String
The string to use as a separator.
- values
Type: System.Collections.Generic.IEnumerable<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.
Exceptions
| Exception | Condition |
|---|---|
| ArgumentNullException | values is nulla null reference (Nothing in Visual Basic). |
Remarks
If separator is nulla null reference (Nothing in Visual Basic), an empty string (String.Empty) is used instead. If any member of values is nulla null reference (Nothing in Visual Basic), an empty string is used instead.
Join<T>(String, IEnumerable<T>) is a convenience method that lets you concatenate each member of an IEnumerable<T> collection without first converting them to strings. The string representation of each object in the IEnumerable<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<T> object that contains a number of Animal objects. The Enumerable.Where extension method is called to extract the Animal objects whose Order property equals "Rodent". The result is passed to the Join<T>(String, IEnumerable<T>) method.
Imports System.Collections.Generic
Public Class Animal
Public Kind As String
Public Order As String
Public Sub New(ByVal kind As String, ByVal 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 Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
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"))
outputBlock.Text &= output & vbCrLf
End Sub
End Module
' The example displays the following output:
' Squirrel Capybara
using System;
using System.Collections.Generic;
using System.Linq;
public class Animal
{
public string Kind;
public string Order;
public Animal(string kind, string order)
{
this.Kind = kind;
this.Order = order;
}
public override string ToString()
{
return this.Kind;
}
}
public class Example
{
public static void Demo(System.Windows.Controls.TextBlock outputBlock)
{
List<Animal> animals = new List<Animal>();
animals.Add(new Animal("Squirrel", "Rodent"));
animals.Add(new Animal("Gray Wolf", "Carnivora"));
animals.Add(new Animal("Capybara", "Rodent"));
string output = String.Join(" ", animals.Where(animal =>
(animal.Order == "Rodent")));
outputBlock.Text += output + "\n";
}
}
// The example displays the following output:
// Squirrel Capybara
Examples
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<T> object of type integer, which it then passes to the Join<T>(String, IEnumerable<T>) method.
Imports System.Collections.Generic
Module Example
Public Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
Dim maxPrime As Integer = 100
Dim primes As List(Of Integer) = GetPrimes(maxPrime)
outputBlock.Text += String.Format("Primes less than {0}:", maxPrime) & vbCrLf
outputBlock.Text += String.Format(" {0}", String.Join(" ", primes)) & vbCrLf
End Sub
Private Function GetPrimes(ByVal maxPrime As Integer) As List(Of Integer)
Dim values(maxPrime) As Integer
' Use Sieve of Erathsthenes to determine prime numbers.
For ctr As Integer = 2 To _
CInt(Math.Ceiling(Math.Sqrt(values.GetUpperBound(0))))
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)
Next
Next
Dim primes As New System.Collections.Generic.List(Of Integer)
For ctr As Integer = 2 To values.GetUpperBound(0)
If CInt(values.GetValue(ctr)) = 0 Then primes.Add(ctr)
Next
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
using System;
using System.Collections.Generic;
public class Example
{
public static void Demo(System.Windows.Controls.TextBlock outputBlock)
{
int maxPrime = 101;
List<int> primes = GetPrimes(maxPrime);
outputBlock.Text += String.Format("Primes less than {0}:", maxPrime) + "\n";
outputBlock.Text += String.Format(" {0}", String.Join(" ", primes)) + "\n";
}
private static List<int> GetPrimes(int maxPrime)
{
int[] values = new int[maxPrime + 1];
// Use Sieve of Erathsthenes to determine prime numbers.
for (int ctr = 2; ctr <= (int)Math.Ceiling(Math.Sqrt(values.GetUpperBound(0))); ctr++)
{
if ((int)values.GetValue(ctr) == 1) continue;
for (int multiplier = ctr; multiplier <= maxPrime / 2; multiplier++)
if (ctr * multiplier <= maxPrime)
values.SetValue(1, ctr * multiplier);
}
List<int> primes = new List<int>();
for (int ctr = 2; ctr <= values.GetUpperBound(0); ctr++)
if ((int)values.GetValue(ctr) == 0)
primes.Add(ctr);
return primes;
}
}
// 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
Version Information
Silverlight
Supported in: 5, 4
Silverlight for Windows Phone
Supported in: Windows Phone OS 7.1
Platforms
For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.
Change History
Date |
History |
Reason |
|---|---|---|
January 2011 |
Noted that an empty string is substituted for any null member of the collection. |
Customer feedback. |