Comments on: Functional C#: Using Join and GroupJoin

By: Paul Batum

Paul Batum — Sun, 07 Mar 2010 12:32:41 +0000

I haven’t verified it, but it wouldn’t surprise me if my version (and similarly, Jonas’s) was less efficient. I haven’t investigated how the join operators work under the covers but it certainly seems possible that Mark’s version involves fewer iterations through the list of cars.

Still, hopefully these lists aren’t big and we can go with the easier to read (if perhaps slower) approach

By: Jonas Elfström

Jonas Elfström — Fri, 05 Mar 2010 10:08:10 +0000

@Paul nice catch!

@Mark I think that all of us do that a lot more than we realize. Even while commenting on exactly that, I still overcomplicated above. By being kind and posting your code in public you get the power of a thousand pair programmers. It’s great because both you and the readers are being educated.

By: Mark Needham

Mark Needham — Fri, 05 Mar 2010 07:42:28 +0000

@Jonas, Paul – at first glance it looks like you guys are right, I’ve massively overcomplicated those again, d’oh!

I’m kinda intrigued as to why I’m doing that though – a simpler solution was pointed out for another problem I described a couple of weeks ago as well!

By: Paul Batum

Paul Batum — Fri, 05 Mar 2010 03:44:11 +0000

I’m also wondering if I’m missing something

return years.All(y => cars.Any(c => c.Year == y));

By: Jonas Elfström

Jonas Elfström — Thu, 04 Mar 2010 22:00:25 +0000

And in the same spirit:

var areThereMatchingCars = years.All(year => cars.FirstOrDefault(car => car.Year == year) == null ? false : true);

Am I missing something here?

By: Jonas Elfström

Jonas Elfström — Thu, 04 Mar 2010 21:55:59 +0000

Instead of the GroupJoin couldn’t you, in this case, just Select over the years and output a car if there is one?

var newCars = years.Select(year => cars.FirstOrDefault(car => car.Year == year) ?? new Car {Year=year, Description=”"});