Question

My class:

    public class Foo
    {
        public int A { get; set; }
        public List<Bar> Bars { get; set; }
    }

I’ve got IEnumerable<Foo>. I would like get List<Foo> grouping by A, and get Bars list, which contais all elements at Bars for group.

So final Foo.Bars should contains all elements of Bar at group

Is it possible with linq?

Answer 1

var result = foos.GroupBy(f => f.A)
                 .SelectMany(grp => grp.Select(f => f.Bars));

As Rawling has mentioned, this returns not an IEnumerable<Foo>, so try this:

IEnumerable<Foo> result = 
            foos.GroupBy(f => f.A)
            .Select(grp => new Foo() { 
                A = grp.Key,
                Bars = grp.SelectMany(ff => ff.Bars).Distinct().ToList()
            });

I’m not sure whether you want a distinct list of Bars or not. Note that you may need to override Equals and GetHashCode in class Bar.