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Code Analyzer for C#

There is a newer version: 10.2.0.105762

Why is this an issue?
In the interests of readability, code that can be simplified should be simplified. To that end, there are several ways IEnumerable language integrated queries (LINQ) can be
simplified. This not only improves readabilty but can also lead to improved performance.
How to fix it
Simplify the LINQ expressions:

   Use OfType instead of Select with the as operator to type cast
  elements and then null-checking in a query expression to choose elements based on type. 
   Use OfType instead of using Where and the
  is operator, followed
  by a cast in a Select 
   Use an expression in Any instead of Where(element ⇒ [expression]).Any(). 
   Use the Count or Length properties instead of the Count() method when it’s available (unless you use the
  predicate parameter of the method for filtering). 
   Don’t call ToArray() or ToList() in the middle of a query chain. 

Using Entity Framework may require enforcing client evaluations. Such queries should use AsEnumerable() instead of ToArray() or
ToList() in the middle of a query chain.
Code examples
Noncompliant code example
public void Foo(IEnumerable<Vehicle> seq, List<int> list)
{
    var result1 = seq.Select(x => x as Car).Any(x => x != null);               // Noncompliant; use OfType
    var result2 = seq.Select(x => x as Car).Any(x => x != null && x.HasOwner); // Noncompliant; use OfType before calling Any
    var result3 = seq.Where(x => x is Car).Select(x => x as Car);              // Noncompliant; use OfType
    var result4 = seq.Where(x => x is Car).Select(x => (Car)x);                // Noncompliant; use OfType
    var result5 = seq.Where(x => x.HasOwner).Any();                            // Noncompliant; use Any([predicate])

    var num = list.Count();                                                    // Noncompliant; use the Count property
    var arr = seq.ToList().ToArray();                                          // Noncompliant; ToList is not needed
    var count = seq.ToList().Count(x => x.HasOwner);                           // Noncompliant; ToList is not needed
}

Compliant solution
public void Foo(IEnumerable<Vehicle> seq, List<int> list)
{
    var result1 = seq.OfType<Car>().Any();
    var result2 = seq.OfType<Car>().Any(x => x.HasOwner);
    var result3 = seq.OfType<Car>();
    var result4 = seq.OfType<Car>();
    var result5 = seq.Any(x => x.HasOwner);

    var num = list.Count;
    var arr = seq.ToArray();
    var count = seq.Count(x => x.HasOwner);
}

Resources
Documentation

   Language Integrated Queries in C#