Your Favorite LINQ-to-Objects Queries [closed]

Question

With LINQ, a lot of programming problems can be solved more easily - and in fewer lines of code.

What are some the best real-world LINQ-to-Objects queries that you've written?

(Best = simplicity & elegance compared to the C# 2.0 / imperative approach).

Answer 1

Filter out null items in a list.

var nonnull = somelist.Where(a => a != null);

Create a dictionary where the key is the value of a property, and the value is the number of times that property appears in the list.

var countDictionary = somelist
    .GroupBy(a => a.SomeProperty)
    .ToDictionary(g => g.Key, g => g.Count());

Answer 2

LINQ is merely the addition of some functional programming concepts to C#/VB. Hence, yes, most things tend to get much easier. C# 2.0 actually had some of this -- see the List methods, for instance. (Although, anonymous method syntax in C# 2.0 was too verbose.)

Here's one little example:

static readonly string badChars = "!@#$%^&*()";
bool IsUserNameValid(string userName) {
  return userName.Intersect(badChars).Any();
}