LINQ LIST: Distinct method extension

While operating with collections, sometime we would like to perform Distinct on column, to achieve this we need to write the extension method.

public static class StaticDistinct
       public static IEnumerable<TSource> DistinctBy<TSource, TKey>
        (this IEnumerable<TSource> source, Func<TSource, TKey> keySelector)
              HashSet<TKey> knownKeys = new HashSet<TKey>();
              foreach (TSource element in source)
                    if (knownKeys.Add(keySelector(element)))
                         yield return element;

var distinctUsers = users.DistinctBy(x => x.EmailId).ToList();

This example also demostrate what are extension methods and syntax of extension method.

Extension Methods:

#1) These are static methods, so these method should be surronded by static class

#2) These method signature would start this keyword. Let’s say you want to write extension method to string then the method would be some thing like below.

 public static string ImExtensionMethod(this string value)
   return "Hurray! I am EXTENSION method";

  string whoAreYou = "Hello";

By now you should be knowing why did we define DISTINCTBY as extension method

Happy Kooding…. Hope this helps!


Find No of Lines in Files (In a directory & sub directory)

Hi All,

In this article, we will perform below tasks & this code base is window forms

1.       Find  list of files present in a directory & sub directory without calling function(s) recursively i.e. avoid recursive function

2.       Calculate no of lines of code available in all files under a directory & sub directory

This code is Window Form code:

1.       Open a new windows form application

2.       Add following  controls to the form1,assign controls NAME & TEXT properties respectively

a.       Label  à Name: lblPath, Text: Files Path

b.      Label à Name: lblFileTypes, Text: File Types

c.       Label à Name: lblLinesCount, Text : No of Lines

d.      Label à Name: lblFilesCount, Text : No of Files

e.      Textbox à Name : txtPath, Text:

f.        Button à Name: btnCalculate, Text: Calculate Lines

3.       Declare below global variable inside the form1 class

int linesCount = 0;

4.       Add below code in btnCalculate click event with inline comments to each code statement

private void btnCalculate_Click(object sender, EventArgs e)


/* below code, declares array list object & call GetAllFiles which will take folder path which is to be crawled & this function returns all files in the directory & sub directories */

ArrayList filesList = GetAllFiles(txtPath.Text.ToString());

/* below code, for loop is to read each file from filesList object & sum no of files present in each file */

foreach (string fileName in filesList)


/* below code, find all lines present in a files */

string[] lines = File.ReadAllLines(fileName);

/* below code, finds lines count & add it to global linesCount variable*/

linesCount += lines.Length;


/* below code, assigns not of lines present in all files to label  */

lblLinesCount.Text += Convert.ToString(linesCount.ToString());

/* below code, assigns total files crawled by our code */

lblFilesCount.Text += Convert.ToString(filesList.Count.ToString());


5.       Now let’s add GetAllFiles function, with inline comments to each code statements

/* below function takes director path to be crawled */

private ArrayList GetAllFiles(string directory)


/* below code, declares Arraylist object */

ArrayList totalFilesList = new ArrayList();

/* below code, does a preliminary checks to see if the directory path is not empty, if it is empty simply returns i.e. exit the function execution*/

if (directory == string.Empty)

return totalFilesList;

/* below code, creates search option object to crawl all sub directories in a parent directory. The beauty of this is, by using this we can avoid calling of function recursively to find sub directories */

SearchOption sop = SearchOption.AllDirectories;

/* below code, get all files in a directories & sub directories with the extensions .cs

Directory.GetFiles returns files list & take 3 parameters 1. Root directory path 2. Files to be read with extension .cs 3. SearchOption object */

string[] files = Directory.GetFiles(directory, “*.cs”, sop);

/* below code, add up the filesList to main arraylist object */


/* below code, return arraylist with list of files */

return totalFilesList;


6.       Now execute & the output

Happy Kooding… Hope this helps!