How to handle nulls in LINQ when using Min or Max?

Question

I have the following Linq query:

result.Partials.Where(o => o.IsPositive).Min(o => o.Result) 

I get an exception when result.Partials.Where(o => o.IsPositive) does not contains elements. Is there an elegant way to handle this other than splitting the operation in two and checking for null? I have a class full of operations like this one.

EDIT: The question is related with LINQ to Objects.

This is the Exception I'm getting (translated it says: The sequence is empty):

Answer 1

A short summary of the calculation of a Min

- No mediation (Exception!)

   var min = result.Partials.Where(o => o.IsPositive).Min(o => o.Result); 

This is your case: if there are no matching elements, then the Min call will raise an exception (InvalidOperationException).

- With DefaultIfEmpty() -- still troublesome

 var min = result.Partials.Where(o => o.IsPositive)                           .Select(o => o.Result)                           .DefaultIfEmpty()                           .Min(); 

DefaultIfEmpty will create an enumeration over the 0 element, when there are no elements in the list. How do you know that 0 is the Min or if 0 stands for a list with no elements?

- Nullable values; A better solution

   var min = result.Partials.Where(o => o.IsPositive)                             .Min(o => (decimal?)o.Result); 

Here Min is either null (because that's equal to default(decimal?)) or the actual Min found.

So a consumer of this result will know that:

1. When result is null then the list had no elements
2. When the result is a decimal value then the list had some elements and the Min of those elements is that returned value.

However, when this doesn't matter, then min.GetValueOrDefault(0) can be called.

Answer 2

You can use the DefaultIfEmpty method to ensure the collection has at least 1 item:

result.Partials.Where(o => o.IsPositive).Select(o => o.Result).DefaultIfEmpty().Min();