Creating Groups out of two different lists - list

Question

I guess this is an easy one but I have no clue how to do this.
I have two lists of Persons
List<Person> specificPersons
List<Person> allPersons
I would like to create groups out of the two complete lists like the following with linq.
IEnumerable<IGrouping<string, Person>> personsGroups
The string will be any custom string. I would use this to display both lists separated by a group header in a Windows 8.1 Metro Application ListView using a CollectionViewSource binding to the IEnumerable.

Answer 1

You can do something like this:
string headerSpecific = "Specific";
string headerAll = "All";
var query =
specificPersons.GroupBy(_ => headerSpecific )
.Union(
allPersons.GroupBy(_ => headerAll));
Note you have other ways to accomplish similar functionality (although not matching your question's requirements), for instance using anonymous types instead of groups:
var query =
specificPersons.Select(p => new { Header = headerSpecific, p})
.Union(
allPersons.Select(p => new { Header = headerAll, p}));

Answer 2

I would suggest adding a Group property to Person, which you can set via a simple loop on each of your lists. Then you can do this:
IEnumerable<IGrouping<string, Person>> personsGroups = specificPersons.Concat(allPersons).GroupBy(p => p.Group);
Note that this would not make sense if Person is a domain entity and/or exists in your database. Since these groups are for display purposes, use a view model (e.g. PersonViewModel) and add the Group property to that model to avoid changing your domain model.