Filter values in linq orderby

Question

Is there a way to filter the value -1 (from the IndexOf when txt not found in item) in the below query?

var sortedArray = array.OrderBy (item => item.IndexOf(txt)).ToArray();

Any pointers will be helpful.

If I use Where, it would be using IndexOf twice, is there a way to use IndexOf only once?

Answer 1

To avoid having to do the same IndexOf twice you can do:

var sortedArray = (from a in array
                  let i = a.IndexOf("txt")
                  where i >= 0
                  orderby i
                  select a).ToArray();

Answer 2

You can use Where to do your predicate, and then OrderBy later on.

var sortedArray =
    array.Where   (item => item.IndexOf("txt") != -1)
         .OrderBy (item => item.IndexOf("txt")).ToArray();

Answer 3

The easiest way is just to put a .Where() clause first.

var sortedArray = array.Where (item => item.IndexOf(txt) != -1)
                       .OrderBy (item => item.IndexOf(txt))
                       .ToArray();

This will probably cause a notable performance impact on large arrays or large data in the array, though, since you're now searching for it twice.