c# - Get all combinations of items in an array -

i have text files in folder such f1.txt,f2.txt,....f15.txt. want combination of them has length 2.

the final result should

{f1.txt, f2.txt}, {f1.txt, f3.txt}....

i used code

 static ienumerable<ienumerable<t>>  getkcombs<t>(ienumerable<t> list, int length) t : icomparable  {         if (length == 1) return list.select(t => new t[] { t });         return getkcombs(list, length - 1)             .selectmany(t => list.where(o => o.compareto(t.last()) > 0),                 (t1, t2) => t1.concat(new t[] { t2 }));  } 

then call main method.

string[] files = directory.getfiles(@"c:\users\downloads\samples", "*.txt"); ienumerable<ienumerable<string>> filescombination = getkcombs(files, 2); 

but why got nothing?

edit:

        foreach(var x in filescombination)         {             console.writeline(x);         } 

in immediate window, have

?x           {system.linq.enumerable.concatiterator<string>}             first: null             second: null 

check 'files' contains list of files expect.

the method working expected. tested in small test app:

class program {     static void main(string[] args)     {         list<int> list = new list<int> { 1, 2, 3, 4 };          ienumerable<ienumerable<int>> result = getkcombs(list, 2);          foreach (var line in result)         {             foreach (var item in line)             {                 console.write("{0}, ", item);             }             console.writeline();         }          console.readkey();     }      static ienumerable<ienumerable<t>> getkcombs<t>(ienumerable<t> list, int length) t : icomparable     {         if (length == 1) return list.select(t => new t[] { t });         return getkcombs(list, length - 1)             .selectmany(t => list.where(o => o.compareto(t.last()) > 0),                 (t1, t2) => t1.concat(new t[] { t2 }));     } } 

edit:

in code have:

    foreach(ienumerable<string> x in filescombination)     {         console.writeline(x);     } 

when console.writeline(x) it's equivalent console.writeline(x.tostring()). default behaviour of tostring() show name of object.

the reason why in debug mode first: null , second: null because of deferred execution. ienumerable object doesn't yet know value is, until try use values, tolist() or iterator, example.