Using MinBy and MaxBy in C# 10 / .NET 6

Microsoft made a couple new additions to LINQ as part of the C# 13 / .NET 9 release a few weeks ago, and, since I happen to really like LINQ, I wrote about how to use them. That got me thinking about other recent additions I might've missed in the last few releases, so I started looking back. And whatdya know, we got a slew of updates to LINQ in C# 10 / .NET 6 a few years ago.

Let's take a look at two of them - MaxBy and MinBy - right after a brief overview of what we had before. Makes it a little easier to appreciate the new stuff!

Finding a Simple 'Max'

Normally, when we want to find the max or min value of some collection of primitive types, then a simple call to Max or Min will do. With a list of integers, for example, the max number is the highest. No surprise there.

var maxNumber = new[] { 4, 3, 1, 17, 9, 0 }.Max();
Console.WriteLine($"The max number is: {maxNumber}");

// The max number is: 17

Implementing IComparer<T>

For other types, we can implement the IComparer<T> interface, telling Max and Min what to use for the comparison. It can be really complex, or as simple as looking at one property:

internal record Employee(string Name, string Dept, decimal Salary,
    DateOnly HireDate, int SecurityLevel) : IComparable<Employee>
{
    public int CompareTo(Employee? other)
    {
        if (other == null)
            return 1;

        return Salary > other.Salary ? 1 : Salary < other.Salary ? -1 : 0;
    }
}

In this case, the max or min Employee is just whoever makes the most or least:

var employees = new List<Employee>
{
    new("Ed",  "Accounting",  78_000, new(2010,3,2), 1),
    new("Ned", "Accounting", 120_000, new(2000,2,6), 2),
    new("Ted", "Accounting",  94_000, new(2020,1,1), 0),
    new("Bob", "Accounting",  55_000, new(2015,7,2), 3)
};

var max = employees.Max();  // Ned
var min = employees.Min();  // Bob
Console.WriteLine($"{max!.Name} makes the most at {max.Salary:C}, " +
    $"while {min!.Name} makes the least at {min.Salary:C}.");

// Ned makes the most at $120,000.00, while Bob makes the least at $55,000.00.

Using MinBy and MaxBy

The new MaxBy and MinBy methods let us specify a property to sort by, which allows for more flexbility in simple cases. We can sort employees by hire date, for example, and then sort by their security level immediately after:

var newestHire = employees.MaxBy(e => e.HireDate);
var oldestHire = employees.MinBy(e => e.HireDate);

Console.WriteLine($"{newestHire!.Name} was the newest hire on {newestHire.HireDate}, " +
    $"while {oldestHire!.Name} was hired long ago on {oldestHire.HireDate}.");

// Ted was the newest hire on 1/1/2020, while Ned was hired long ago on 2/6/2000.


var mostSecurePersonnel = employees.MaxBy(e => e.SecurityLevel);
var leastSecurePersonnel = employees.MinBy(e => e.SecurityLevel);

Console.WriteLine($"{mostSecurePersonnel!.Name} has the highest security level, " +
    $"while {leastSecurePersonnel!.Name} has the lowest.");

// Bob has the highest security level, while Ted has the lowest.

Before, if we weren't implementing the interface, then we had to order the collection first and grab the first item, like this:

var maxBySalary = employees.OrderByDescending(e => e.Salary).First();
var minBySalary = employees.OrderBy(e => e.Salary).First();

That isn't much longer, but MaxBy and MinBy just read better. The new methods make it easier to tell at a glance what the code is doing, and that's not a trivial thing. We don't have to reason out what the OrderBy is doing, nor do we have to open the class and investigate the CompareTo method.

Like anything though, there's limitations. Since we can only specify one property, we still need something like this to consider multiple properties:

var mostCompensatedEmployee = employees
    .OrderByDescending(e => e.Salary)   // what if two people earn the same salary?
    .ThenByDescending(e => e.Overtime)  // then we should consider overtime too
    .ThenByDescending(e => e.Bonus)     // and their bonus, as a final tie-breaker
    .First();

We can also use methods that provide a useful value, like the Count() method on a collection. One more example and then I'm done! Here's two companies, and a quick use of MaxBy to grab the one with more employees:

var warnerEmps = new Company("Warner Bros", new List<Employee>
{
    new("Yakko", "IT",  78_000, new(2010,3,2), 1),
    new("Wakko", "IT", 90_000,  new(2000,2,6), 2),
    new("Dot", "IT", 90_000,  new(2000,2,6), 2),
});

var acmeEmps = new Company("Acme Inc", new List<Employee>
{
    new("Wile E Coyote", "IT",  78_000, new(2010,3,2), 1),
    new("Road Runner", "IT", 90_000,  new(2000,2,6), 2),
});

var largestCompany = new[] { warnerEmps, acmeEmps }.MaxBy(c => c.Employees.Count());

Console.WriteLine($"{largestCompany!.Name} is the largest company.");

// Warner Bros is the largest company.

I, for one, welcome any and all additions to LINQ, and can imagine that in many situations MaxBy and MinBy will make the code we write a little cleaner. Every bit counts!

Learning More

If you found this content useful, and would like to learn more about a variety of C# features, check out my CSharpDotNetFeatures repo, where you'll find links to plenty more blog posts and practical examples!

GitHub - grantwinney/CSharpDotNetExamples: Discovering and learning about the various features of the C# programming language and .NET Framework.

Discovering and learning about the various features of the C# programming language and .NET Framework. - GitHub - grantwinney/CSharpDotNetExamples: Discovering and learning about the various featur…

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