How to check if a string is unique in a file and if it is write to another file in C#? -

i have 2 files f1.txt , f2.txt. f1.txt contains contents like

u1,u2 u1,u5 u3,u4 u2,u1 u3,u4 

essentially u1,u2 , u2,u1 mean same . want write distinct contents file f2.txt i.e. after writing f2.txt should contain

u1,u2 u1,u5 u3,u4 

i tried below did not work out.

using system; using system.collections.generic; using system.io; using system.linq; using system.text; using system.threading.tasks;  namespace stringinfiletechchef {     class program     {         static void main(string[] args)         {             string line = "";             using (streamreader sr = new streamreader(@"c:\users\chiranjib\desktop\f1.txt"))             {                 while((line=sr.readline()) !=null)                 {                     if (!file.readalltext(@"c:\users\chiranjib\desktop\f2.txt").contains(line))                     {                         //char[] array = line.tochararray();                         //array.reverse(array);                         //string temp = new string(array);                          string temp1 = line.substring(0, 2);                         string temp2 = line.substring(3, 2);                          if (!file.readalltext(@"c:\users\chiranjib\desktop\f2.txt").contains(temp2 + "," + temp1))                         {                             using (streamwriter sw = new streamwriter(@"c:\users\chiranjib\desktop\f2.txt"))                             {                                 sw.writeline(line);                                 console.writeline(line);                             }                         }                     }                 }             }             console.readkey();         }     } } 

what missing ? how achieve scenario.

here how it:

take each line , split string[]

sort string[]

join string[] string

take distinct strings

var distinct = file.readlines("textfile2.txt")     .select(l => string.join(",", l.split(',').orderby(i => i)))     .distinct();  file.writealllines("f2.txt", distinct);