Getting the max value of a property by category in a list of objects

Question

For list of objects of class Animal

public class Animal
{
    public int id { get; set; }
    public string name{ get; set; }
    public string category { get; set; }
    public int avg_lifespan { get; set; }
}

How can I return the animals with the highest avg_lifespan by category?

e.g. I have a dataset with 50 animals within 5 categories, I want to return, for each category, the animal with the highest average lifespan.

So far, I have this LINQ statement that returns the distinct categories:

var categories = animals.SelectMany(e => e.category).Distinct();

My idea was to iterate through the list of Animal objects, and for each animal in the list, increment some value with the corresponding animal's average lifespan. How can I do this more elegantly ?

[`GroupBy`](https://learn.microsoft.com/en-us/dotnet/api/system.linq.enumerable.groupby?view=netcore-3.1) — Heretic Monkey, Jun 19 '20 at 16:46
Why is `avg_lifespan` a `string`? It seems like that should be some kind of numeric type for comparisons. — itsme86, Jun 19 '20 at 16:52
@HereticMonkey thank you, it slipped my mind that that is what I was looking for! — crystyxn, Jun 19 '20 at 16:54

score 0 · Answer 1 · answered Jun 19 '20 at 17:15

U can also use groupby, select and aggregate function in linq as follows

   static void Main()
    {
        IEnumerable<Animal> animals =
            new List<Animal>()
            {
                new Animal{ category="A",avg_lifespan=1},
                new Animal{ category="A",avg_lifespan=2},
                new Animal{ category="B",avg_lifespan=3},
                new Animal{ category="B",avg_lifespan=5},
                new Animal{ category="B",avg_lifespan=7}

            }
            .GroupBy(x => x.category)
            .Select(x => x.Aggregate((f, s) => f.avg_lifespan >= s.avg_lifespan ? f : s));

        foreach (var animal in animals)
        {
            Console.WriteLine($"category: {animal.category} \t avg_lifespan: {animal.avg_lifespan}");
        }
    }

Getting the max value of a property by category in a list of objects

1 Answers1