Example. In this program, we include the System.Linq namespace to get access to the Concat method. Two arrays are created upon execution of the Main method.
LINQThen: We call the Concat method twice, in different orders, and display the results.
Tip: If you have ever needed to write custom code to combine two arrays or Lists into a single one, the Concat method might be useful.
ListPlease note: This might cause some performance degradation because of the flexibility and implementation of the extension methods.
Extension C# program that uses Concat extension
using System;
using System.Linq;
class Program
{
static void Main()
{
int[] array1 = { 1, 3, 5 };
int[] array2 = { 0, 2, 4 };
// Concat array1 and array2.
var result1 = array1.Concat(array2);
foreach (int value in result1)
{
Console.WriteLine(value);
}
Console.WriteLine();
// Concat array2 and then array1.
var result2 = array2.Concat(array1);
foreach (int value in result2)
{
Console.WriteLine(value);
}
}
}
Output
1
3
5
0
2
4
0
2
4
1
3
5
List example. To use Concat, you can combine two collections that implement IEnumerable. This includes the List type or the array type.
Info: You can combine a List and an array or two Lists. The element type (string) of both collections must be the same.
Return: Concat returns an IEnumerable type. The "var result" in the code is of that type.
Also: You can convert an IEnumerable back into a List with the ToList extension method.
ToList C# program that uses Concat method on Lists
using System;
using System.Collections.Generic;
using System.Linq;
class Program
{
static void Main()
{
List<string> list1 = new List<string>();
list1.Add("dot");
list1.Add("net");
List<string> list2 = new List<string>();
list2.Add("perls");
list2.Add("!");
var result = list1.Concat(list2);
List<string> resultList = result.ToList();
foreach (var entry in resultList)
{
Console.WriteLine(entry);
}
}
}
Output
dot
net
perls
!
A summary. If you have two Lists, you can use the Concat method to combine them. For optimal performance, however, using a method such as AddRange would be better if you need a List result.