How to get an array of members of an array

Question

Suppose I have a class

public class Foo
{
    public Bar Bar { get; set; }
}

Then I have another class

public class Gloop
{
    public List<Foo> Foos { get; set; }
}

What's the easiest way to get a List<Bar> of Foo.Bars?

I'm using C# 4.0 and can use Linq if that is the best choice.

UPDATE:

Just for a little dose of reality, the reason for this is that I have a Windows Service class that contains an inner ServiceBase derived class as a property. So I end up with code like this:

public class Service
{
    public ServiceBase InnerService { get; set; }
}

public class ServiceHost
{
    private List<Service> services = new List<Service>();
    static void Main()
    {
         // code to add services to the list
         ServiceBase.Run(services.Select(service => service.InnerService).ToArray());
    }
}

I didn't think it was obvious :) I was stumped actually ..lol. Anyways time to goto bed... — VoodooChild
– VoodooChild, Commented Jun 10, 2010 at 6:25

Jon Skeet · Accepted Answer · 2010-06-10 06:20:24Z

2

This one's simple, if I've understood you rightly:

List<Foo> foos = gloop.Foos; // Or wherever you're getting it from
List<Bar> bars = foos.Select(foo => foo.Bar)
                     .ToList();

If you only need an IEnumerable<Bar> you can just use Select without the call to ToList. Of course you don't need the foos local variable if you don't want it - you can just have a single statement. I've only separated them out in case you've got an existing List<Foo> or Foo[] (you mention arrays in your subject line).

edited Jun 10, 2010 at 6:20

answered Jun 10, 2010 at 6:12

Jon Skeet

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11 Comments

Erik Funkenbusch Over a year ago

What's more efficient, the Select with lambda, or something like (from b in gloop.Foos select b.Bar).ToList()

Jon Skeet Over a year ago

@Mystere Man: They end up as the same IL, but I don't see any reason for using a query expression when you're just doing a simple projection. It's extra clutter.

mynameiscoffey Over a year ago

Since he mentioned Linq, the Linq equivalent for the second statement should be: List<Bar> bars = (from f in foos.Bar select f).ToList();

Erik Funkenbusch Over a year ago

Good point Jon, as usual, you're the voice of reason and wisdom ;)

Jon Skeet Over a year ago

@mynameiscoffey: Why? LINQ doesn't necessitate the use of query expressions IMO. We're still using LINQ to Objects, but taking the simplest syntax for the situation, IMO. Not to mention the fact that your query wouldn't work as written ;)

|

carlmon · Accepted Answer · 2010-06-10 06:14:05Z

1

var bars = gloop.Foos.Select(foo => foo.Bar);

answered Jun 10, 2010 at 6:14

carlmon

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3 Comments

carlmon Over a year ago

As stated in another answer, this only returns IEnumerable<Bar>. Use ToList() if you need it as List<Bar>.

VoodooChild Over a year ago

did you forget to add the "ToList()"? or is that the return type of the Select call?

carlmon Over a year ago

Yes, I forgot the ToList() in my initial (quick) answer. IList adds some additional functionality to IEnumerable, like insert/delete which may be inappropriate given the source.

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