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Some Common Operations using List - Part I

Posted by: Suprotim Agarwal , on 1/15/2010, in Category LINQ
Views: 106003
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
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Author
Suprotim Agarwal, MCSD, MCAD, MCDBA, MCSE, is the founder of DotNetCurry, DNC Magazine for Developers, SQLServerCurry and DevCurry. He has also authored a couple of books 51 Recipes using jQuery with ASP.NET Controls and a new one recently at The Absolutely Awesome jQuery CookBook.

Suprotim has received the prestigous Microsoft MVP award for nine times in a row now. In a professional capacity, he is the CEO of A2Z Knowledge Visuals Pvt Ltd, a digital group that represents premium web sites and digital publications comprising of Professional web, windows, mobile and cloud developers, technical managers, and architects.

Get in touch with him on Twitter @suprotimagarwal, LinkedIn or befriend him on Facebook



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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"}