C# Linq Query group by check if result is null

Question

If I have a class like this

public class Test
{
   public string Id {get; set;}
   public string Name {get; set;}
   public int Value {get; set;}
}

and then:

List<Test> values = new List<Test>(); // this contains let's say 10 items

and I do like this:

var grouped = values.Where(x=>x.Value > 10).GroupBy(x=>x.Name);

My question is how can I check if grouped == null? Or how can I check that there are no groupings that matches that criteria?

I am asking because if I do like this:

if (grouped == null) // this is false although the linq yielded no results
{

}

Answer 1

You can use method Any():

var anyItems = grouped.Any();

You do not need to check for null, because grouping would return an empty collection instead of null

Answer 2

You could check if there is no groups, like below:

var anyGroups = grouped.Any();

If there is at least one group, the extension method called Any will return true. Otherwise it will return false.

According to MSDN, this is the signature of the method GroupBy:

public static IEnumerable<IGrouping<TKey, TSource>> GroupBy<TSource, TKey>(
    this IEnumerable<TSource> source,
    Func<TSource, TKey> keySelector)

It is clear from the above that this method returns a sequence of items that implement the IGrouping interface. (IGrouping Represents a collection of objects that have a common key). An easy way to find out if a sequence contains elements, is using the enumerable's extension method called Any.

Furthermore this is a O(1) operation -using the Any method and not passing any predicate in it. While using the enumerable's extension method called Count, in some cases is an O(n) operation.