Question

I have the following LINQ expression:

pantry = (from p in items
          group p by p.IngredientId into g
          select new PantryItem() { IngredientId = g.Key, Amt = g.Sum(p => p.Amt) });

Basically, I’m trying to remove duplicates from an array by summing up their total amounts. So if I have 2 items of IngredientId x, one with Amt 5 and the other with Amt 10, I want a single item of Ingredient x with the Amt 15. Easy enough right?

Now, to completely break everything, Amt is actually a float?, not a float. However, when I Sum a group with all null amounts, I get 0.0 instead of null.

Here’s what I want:

x - null
x - null
y - 5
y - 10
z - 10
z - null

Should convert to:

x - null
y - 15
z - 10

But instead I get:

x - 0.0
y - 15
z - 10

Is there a way to re-work my LINQ query to facilitate this? Hopefully my question is clear enough 🙂

Answer 1

You have 2 choices:

1. Write your own implementation of Sum
2. Check if all values are null, then return null, otherwise return sum, e.g.:

---

pantry = (from p in items
          group p by p.IngredientId into g
          select new PantryItem() 
          { 
              IngredientId = g.Key, 
              Amt = g.Any(p => p.Amt.HasValue) ? g.Sum(p => p.Amt) : null 
          });

NOTE: 2^nd query will enumerate twice.