Some Common Operations using List - Part I

Posted by: Suprotim Agarwal , on 1/15/2010, in Category LINQ
Views: 91298
Abstract: In this article, I will demonstrate some common operations on List using LINQ
Some Common Operations using List<string> - Part I
 
I have been writing some articles in the past where I try and demonstrate the capabilities of LINQ using some common examples. Some of these articles are:
In this article and the next one, I will demonstrate some common operations on List<string> using LINQ. I assume that you are familiar with LINQ.
Here are the sample List<string> for demonstration purposes. The VB.NET code has been converted using a conversion tool and accuracy has not been tested.
C#
List<string> lstOne = new List<string>() { "January", "February", "March"};
List<string> lstTwo = new List<string>() { "January", "April", "March"};
List<string> lstThree = new List<string>() { "January", "April", "March", "May" };
List<string> lstFour = new List<string>() { "Jan", "Feb", "Jan", "April", "Feb" };
IEnumerable<string> lstNew = null;
VB.NET
Dim lstOne As New List(Of String) (New String() {"January", "February", "March"})
Dim lstTwo As New List(Of String) (New String() {"January", "April", "March"})
Dim lstThree As New List(Of String) (New String() {"January", "April", "March", "May"})
Dim lstFour As New List(Of String) (New String() {"Jan", "Feb", "Jan", "April", "Feb"})
Dim lstNew As IEnumerable(Of String) = Nothing
We will be printing the results on the console using a simple method shown here:
C#
static void PrintList(IEnumerable<string> str)
{
    foreach (var s in str)
        Console.WriteLine(s);
    Console.WriteLine("-------------");
}
VB.NET
Shared Sub PrintList(ByVal str As IEnumerable(Of String))
      For Each s In str
            Console.WriteLine(s)
      Next s
      Console.WriteLine("-------------")
End Sub
Let us get started.
1. Display common elements between two List<string>
 
Use the Enumerable.Intersect method
C#
// Compare two List<string> and display common elements
lstNew = lstOne.Intersect(lstTwo, StringComparer.OrdinalIgnoreCase);
PrintList(lstNew);
VB.NET
lstNew = lstOne.Intersect(lstTwo, StringComparer.OrdinalIgnoreCase)
PrintList(lstNew)
OUTPUT
January_March
2. Display elements found in one List<string> but not in the other
 
Use the Enumerable.Except method
C#
// Compare two List<string> and display items of lstOne not in lstTwo
lstNew = lstOne.Except(lstTwo, StringComparer.OrdinalIgnoreCase);
PrintList(lstNew);
VB.NET
lstNew = lstOne.Except(lstTwo, StringComparer.OrdinalIgnoreCase)
PrintList(lstNew)
Note: The StringComparer.OrdinalIgnoreCase performs a case-insensitive ordinal string comparison
OUTPUT
February
3. Display distinct elements from a List<string>
 
Use the Enumerable.Distinct method
C#
// Unique List<string>
lstNew = lstFour.Distinct(StringComparer.OrdinalIgnoreCase);
PrintList(lstNew)
VB.NET
lstNew = lstFour.Distinct(StringComparer.OrdinalIgnoreCase)
PrintList(lstNew)
OUTPUT
Jan_Feb_April
4. Convert all elements of a List<string> to UpperCase
 
Use the List.ConvertAll method
C#
// Convert elements of List<string> to Upper Case
lstNew = lstOne.ConvertAll(x => x.ToUpper());
PrintList(lstNew);
VB.NET
lstNew = lstOne.ConvertAll(Function(x) x.ToUpper())
PrintList(lstNew)
OUTPUT
MonthsInCaps
5. Concatenate and Sort two List<string>
 
Use the Enumerable.Concat method
C#
// Concatenate and Sort two List<string>
lstNew = lstOne.Concat(lstTwo).OrderBy(s => s);
PrintList(lstNew);
VB.NET
lstNew = lstOne.Concat(lstTwo).OrderBy(Function(s) s)
PrintList(lstNew)
OUTPUT
AtoM
6. Concatenate Unique Elements of two List<string>
 
C#
// Concatenate Unique Elements of two List<string>
lstNew = lstOne.Concat(lstTwo).Distinct();
PrintList(lstNew);
VB.NET
lstNew = lstOne.Concat(lstTwo).Distinct()
PrintList(lstNew)
OUTPUT
JtoA
7. Reverse a List<string>
 
Use the List.Reverse method
C#
// Reverse a List<string>
lstOne.Reverse();
PrintList(lstOne);
VB.NET
lstOne.Reverse()
PrintList(lstOne)
OUTPUT
MtoJ
8. Search a List<string> and Remove the Search Item from the List<string>
Use the List.RemoveAll method
C#
// Search a List<string> and Remove the Search Item
// from the List<string>
int cnt = lstFour.RemoveAll(x => x.Contains("Feb"));
Console.WriteLine("{0} items removed", cnt);
PrintList(lstFour);
VB.NET
Dim cnt As Integer = lstFour.RemoveAll(Function(x) x.Contains("Feb"))
Console.WriteLine("{0} items removed", cnt)
PrintList(lstFour)
OUTPUT
ItmesRemoved
So these were some common List<string> operations. In the next article[UPDATE: The article is online Some Common Operations using List<string> - Part II], we will see some more advanced operations on the List<string>. Stay tuned! The entire source code of this article can be downloaded over here
I hope you liked this article and I thank you for viewing it.
If you liked the article,  Subscribe to the RSS Feed or Subscribe Via Email
Give a +1 to this article if you think it was well written. Thanks!
Recommended Articles
Suprotim Agarwal, ASP.NET Architecture MVP, MCSD, MCAD, MCDBA, MCSE, is the CEO of A2Z Knowledge Visuals Pvt. He primarily works as an Architect Consultant and provides consultancy on how to design and develop .NET centric database solutions.

Suprotim is the founder and primary contributor to DotNetCurry, DNC .NET Magazine, SQLServerCurry and DevCurry. He has also written an EBook 51 Recipes using jQuery with ASP.NET Controls. and is authoring another one at The Absolutely Awesome jQuery CookBook.

Follow him on twitter @suprotimagarwal


Page copy protected against web site content infringement by Copyscape


User Feedback
Comment posted by Jaipee on Saturday, January 16, 2010 12:00 AM
Very useful stuff
Comment posted by Tareq Saleh on Sunday, January 17, 2010 2:51 AM
Thanks for this article .

Please check the note (OrdinalIgnoreCase = a case-insensitive  not case-sensitive)
Comment posted by Suprotim Agarwal on Sunday, January 17, 2010 3:00 AM
Tareq: Thanks! That was a typo and has been rectified.
Comment posted by Himansu Nayak on Wednesday, December 19, 2012 3:08 AM
It is really a good stuff and very useful.

Thank you very much for this article.
Comment posted by Jamison White on Thursday, July 31, 2014 10:51 AM
You can use the FROM keyword instead of string array.
Replace:
Dim lstOne As New List(Of String) (New String() {"January", "February", "March"})

With:
Dim lstOne As New List(Of String) FROM {"January", "February", "March"}

Post your comment
Name:  
E-mail: (Will not be displayed)
Comment:
Insert Cancel