How to: Find the Set Difference Between Two Lists (LINQ)
This example shows how to use LINQ to compare two lists of strings and output those lines that are in names1.txt but not in names2.txt.
To create the data files
- Copy names1.txt and names2.txt to your solution folder as shown in How to: Combine and Compare String Collections (LINQ).
Example
Class CompareLists
Shared Sub Main()
' Create the IEnumerable data sources.
Dim names1 As String() = System.IO.File.ReadAllLines("../../../names1.txt")
Dim names2 As String() = System.IO.File.ReadAllLines("../../../names2.txt")
' Create the query. Note that method syntax must be used here.
Dim differenceQuery = names1.Except(names2)
Console.WriteLine("The following lines are in names1.txt but not names2.txt")
' Execute the query.
For Each name As String In differenceQuery
Console.WriteLine(name)
Next
' Keep console window open in debug mode.
Console.WriteLine("Press any key to exit.")
Console.ReadKey()
End Sub
End Class
' Output:
' The following lines are in names1.txt but not names2.txt
' Potra, Cristina
' Noriega, Fabricio
' Aw, Kam Foo
' Toyoshima, Tim
' Guy, Wey Yuan
' Garcia, Debra
class CompareLists
{
static void Main()
{
// Create the IEnumerable data sources.
string[] names1 = System.IO.File.ReadAllLines(@"../../../names1.txt");
string[] names2 = System.IO.File.ReadAllLines(@"../../../names2.txt");
// Create the query. Note that method syntax must be used here.
IEnumerable<string> differenceQuery =
names1.Except(names2);
// Execute the query.
Console.WriteLine("The following lines are in names1.txt but not names2.txt");
foreach (string s in differenceQuery)
Console.WriteLine(s);
// Keep the console window open in debug mode.
Console.WriteLine("Press any key to exit");
Console.ReadKey();
}
}
/* Output:
The following lines are in names1.txt but not names2.txt
Potra, Cristina
Noriega, Fabricio
Aw, Kam Foo
Toyoshima, Tim
Guy, Wey Yuan
Garcia, Debra
*/
Some types of query operations in both C# and Visual Basic, such as Except, Distinct, Union, and Concat<TSource>, can only be expressed in method-based syntax.
Compiling the Code
Create a Visual Studio project that targets the .NET Framework version 3.5. By default, the project has a reference to System.Core.dll and a using directive (C#) or Imports statement (Visual Basic) for the System.Linq namespace. In C# projects, add a using directive for the System.IO namespace.
Copy this code into your project.
Press F5 to compile and run the program.
Press any key to exit the console window.