Question

I have two collections, and need to create a new collection from the two collections.

Assume the following class:

public class Widget
{
   property int Id{get;set;}
   property string Label{get;set;}
}

We have two IList classes. I would like to create an Anonymous type with Id, Label, and Exists

So doing this for Id and Label, I have:

var newCol=from w in widgets
           select new {Id=w.Id,Label=w.Label,Exists=????}

Is there a way in Linq I can determine exists without writing the looping code myself here?

Edit

Exists tells us if the Widget is in the second list. So for example one solution I just thought of was:

var newCol=from w in widgets
           select new {Id=w.Id,Label=w.Label,Exists=myWidgets.Contains(w)}

Where my widgets is the second IList.

Answer 1

You can also do this using GroupJoin:

var newCol = widgets.GroupJoin(
    otherWidgets,
    w => w.Id,
    w => w.Id,
    (w, joined) => new { Id = w.Id, Label = w.Label, Exists = joined.Any() });