How do I modifiy this linq query using the lamdba operator?

Question

I have the following linq query:

 var files = (from d in new DirectoryInfo(@"c:\program files").GetDirectories()
                         where d.GetFiles().Count() > 10
                         where d.GetFiles().Count() < 100
                         select d
             );

However, as you can see above, I am calling d.GetFiles().Count() twice, is this where the concept of the => operator comes in handy.

Using the syntax from jdehaan, why can't I do it directly like this:

var files = (from d in new DirectoryInfo(@"c:\program files").GetDirectories()
                         where(x => x.GetFiles().Count() > 10) &&
                         (x.GetFiles().Count() < 100))
                         select d
             );

I know the above is stupid because I could just do my original query with d.GetFiles().Count(), but I am curious on the difference between using Where as opposed to the keyword where.

Answer 1

Use let to assign within the query, like this

var files = (from d in new DirectoryInfo(@"c:\program files").GetDirectories()
   let f = d.GetFiles().Count()
   where f > 10
   where f < 100
   select d
);

As Reed Copsey points out you can merge the two where clauses using &&.

Also, since GetFiles returns an array you can use the Length property instead of the Count method.

  var files = (from d in new DirectoryInfo(@"c:\program files").GetDirectories()
     let f = d.GetFiles().Length
     where f > 10 && f < 100
     select d
  );

Answer 2

Lambda expressions will not help here, but the let keyword may...

var files = from d in new DirectoryInfo(@"c:\program files").GetDirectories()
                  let c = d.GetFiles().Count()
                  where c > 10 && c < 100
                  select d;

Answer 3

With lambda expressions it would look like this:

var files = new DirectoryInfo(@"c:\program files").GetDirectories().
    Where(x => (x.GetFiles().Count() > 10) && (x.GetFiles().Count() < 100));

You also call the GetFiles() twice. The lambda expressions don't help solving it.

EDIT: Beside being ugly, it is really inefficient, prefer the let solution presented in the other answers, this answer was meant to show what it looks like written using lambda expressions.

Have a look at "Paul Williams"'s answer, he showed how to reach the same thing with lambda expressions in a better and nicer way that is semantically equivalent to the let solution.

Answer 4

The answer involving the "let" keyword is probably what you will want to use.

I am providing this alternate answer to show you how "=>" could be used to accomplish the same thing.

First, make sure you are using System.Linq;

var files = new DirectoryInfo(@"c:\program files").GetDirectories().Where(d =>
  {
    int c = d.GetFiles().Count();
    return c > 10 && c < 100;
  });

As you can see, lambda expressions aren't a "better" solution in this case, just different.