Five LINQ Methods in Pictures

If you’re learning LINQ for the first time, it can be daunting to learn all LINQ methods at once. Don’t try it.

Here are the five most common LINQ methods in pictures.

LINQ is the declarative, immutable, and lazy-evaluated way of working with collections in C#. And the most frequently used LINQ methods are Where, Select, Any, GroupBy, and FirstOrDefault.

Let’s work with a list of our favorite movies. Let’s write a Movie class with a name, release year, and a rating.

var movies = new List<Movie>
{
    new Movie("Titanic", 1998, 4.5f),
    new Movie("The Fifth Element", 1997, 4.6f),
    new Movie("Terminator 2", 1991, 4.7f),
    new Movie("Avatar", 2009, 5),
    new Movie("Platoon", 1986, 4),
    new Movie("My Neighbor Totoro", 1988, 5)
};

1. Where

Where returns a new collection with only the elements that meet a given condition.

Where works like a filter on collections. Think of Where as a replacement for a foreach with an if in it.

Let’s filter our list of movies to keep only those with a rating greater than or equal to 4.5.

var favorites = movies.Where(movie => movie.Rating >= 4.5);

This query would be something like this,

We’re using arrows to display our LINQ queries. But, the output of a LINQ query is lazy-evaluated. It means the actual result of a LINQ query is evaluated until we loop through its result.

2. Select

Select applies a function to transform every element of a collection.

Let’s find only the names of our favorite movies.

var namesOfFavorites = movies.Where(movie => movie.Rating >= 4.5)
                             .Select(movie => movie.Name);

This query would be,

3. Any

Any checks if a collection has at least one element matching a condition. Unlike Where and Select, Any doesn’t return a new collection, but either true or false.

Let’s see if we have watched movies with a low rating.

var hasBadMovies = movies.Any(movie => movie.Rating < 2);

This query would be,

4. GroupBy

GroupBy returns a collection of “buckets” organized by a key. Also, GroupBy transforms each bucket of elements.

Let’s count the films with the same rating.

var groupedByRating = movies.GroupBy(movie => movie.Rating,
                            (rating, moviesWithSameRating) => new
                            {
                                Rating = rating,
                                Count = moviesWithSameRating.Count()
                            });

The second parameter of GroupBy is a Func with the grouping key and the elements of each group as parameters. This Func works like a mapping function to transform each group or bucket found.

This query would be,

GroupBy has other use-cases, like grouping by more than one property.

5. First & FirstOrDefault

First and FirstOrDefault return the first element in a collection or the first one matching a condition. Otherwise, First throws an exception and FirstOrDefault returns the default value of the collection type.

Let’s find the oldest film we have watched.

var oldest = movies.OrderBy(movie => movie.ReleaseYear)
                   .First();

This query would be,

Voilà! Those are five LINQ methods we use more often: Where, Select, Any, GroupBy, and FirstOrDefault.

Of course, LINQ has more methods like Aggreate, Intersect, Union, and Except, and new overloads from .NET6. But, you will get your back covered with those five methods.

To learn about LINQ and other methods, check my quick guide to LINQ with examples. All you need to know to start working with LINQ, in 15 minutes or less.

Happy LINQ time!