Another improvement that has been added to the LINQ engine is the DistinctBy method.

This is best explained with an example.

Assume you have the following array:

var ages = new[] { 30, 33, 35, 36, 40, 30, 33, 36, 30, 40 };

How would you get the unique ages in the collection?

The simplest solution is a LINQ expression.

var uniqueAges = ages.Distinct().ToArray();
foreach (var age in uniqueAges)
    Console.Write($"{age} ");

This should print the following:

30 33 35 36 40

We are turning it back into an array because after running Distinct we get back an IEnumerable.

Pretty straightforward.

Now imagine it is not a simple array of numbers, but a collection of objects?

Here we are using our Agent, but this time it is a record (the Name and Age can only be set once)

public record Agent
    public string Name { get; init; }
    public byte Age { get; init; }

Assume we have a collection of Agents:

var agents = new[]
    new Agent() {Name = "Ethan Hunt", Age = 40},
    new Agent() {Name = "James Bond", Age = 40},
    new Agent() {Name = "Jason Bourne", Age = 35},
    new Agent() {Name = "Evelyn Salt", Age = 30},
    new Agent() {Name = "Jack Ryan", Age = 36},
    new Agent() {Name = "Jane Smith", Age = 35},
    new Agent() {Name = "Oren Ishii", Age = 30},
    new Agent() {Name = "Natasha Romanoff", Age = 33}

If we wanted to get a list of Agents with unique ages, you likely have to do it in two passes:

  1. Get the distinct ages
  2. For each distinct age, query the collection and pick the First agent whose age is a match.

This is simplified using the DistinctBy method.

To get a list of all the agents with unique ages, you write this expression:

var distinctlyAgedAgents = agents.DistinctBy(x => x.Age);
foreach (var agent in distinctlyAgedAgents)
    Console.WriteLine($"Agent {agent.Name} is {agent.Age}");

This should print the following:

Agent Ethan Hunt is 40
Agent Jason Bourne is 35
Agent Evelyn Salt is 30
Agent Jack Ryan is 36
Agent Natasha Romanoff is 33

The beauty of this is not only is it concise, but you can also chain methods to do additional things like sorting.

For example we can order the agents by their Name.

var distinctAgents = agents.DistinctBy(x => x.Age).OrderBy(x => x.Name);


Very simple yet very useful addition to the LINQ toolbelt.

The code is in my Github


The new DistinctBy LINQ method allows to select distinct objects from a collection based on a child property.

This is Day 9 of the 30 Days Of .NET 6 where every day I will attempt to explain one new / improved thing in the upcoming release of .NET 6.