Simple .DistinctBy Extension

LINQ’s Distinct extension has largely been a disappointment to me. Sure, it’s nice when I’m working with a collection of integers, but more often than not, I’m working with a collection of objects and don’t have an IEqualityComparer<TSource> available to me. I know I could just create one, but I just want to use a lambda like just about everything else I do with LINQ!

To the internet!, right? I learned I could use the following trick to accomplish what I want:

  .GroupBy(x => x.key)
  .Select(x => x.First());

Works like a charm, but I got tired of dot-GroupBy-dot-Select-ing and adding a comment about what I was doing for future maintainers, and I think it’s a lot better to just chuck it into an extension method.

public static IEnumerable<TSource> DistinctBy<TSource, TKey>(
    this IEnumerable<TSource> source, 
    Func<TSource, TKey> keySelector
            .Select(grp => grp.First());

Ahh, nice! Alternatively, could score this functionality by adding MoreLINQ to your project. On a neat side-note, you can also cherry-pick which MoreLINQ functionality you want by installing individual packages.


Author: Adam Prescott

I'm enthusiastic and passionate about creating intuitive, great-looking software. I strive to find the simplest solutions to complex problems, and I embrace agile principles and test-driven development.

One thought on “Simple .DistinctBy Extension”

  1. I actually found that Distinct is really useful with Entity Framework, since it literally translates to a SQL distinct statement. I definitely ran into the same problems that you did with projects that weren’t using EF though.

Leave a comment

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: