Filtering Null values in Select

Question

I have IQueryable list of objects of type T which I want to transform into objects of type K

List tranformedList = originalList.Select(x => trans         


        

Answer 1

Use Where Instead of Select (Linq).

Where returns the list without null values directly

List tranformedList = originalList.Where(x => x != null).ToList();

Answer 2

You could try a for loop and add the non nulls to the new transformed list.

foreach (var original in originalList)
{
    K transformed = tranform(orignal);
    if (transformed != null)
    {
        tranformedList.Add(transformed);
    }
}

or you could try

        List<K> tranformedList = (from t in
                                      (from o in originalList
                                       select tranform(o))
                                  where t != null
                                  select t).ToList();

I think Nathan's works as well but is less verbose

Answer 3

Can't you just do something like this:

List<K> tranformedList = originalList.Select(x => tranform(x))
                                 .Where(y => y != null) //Check for nulls
                                 .ToList();

Answer 4

What about

    List<K> tranformedList = originalList
                             .Select(x => transform(x))
                             .OfType<K>()
                             .ToList()

Takes care of unboxing an getting rid of nulls at the same time (especially when K is a struct)

David B I dont believe you that your code .Where(y => y != null) works when K is an int! There is NO WAY you will get that code to compile if K is an int!