在C＃中，如何获取列表属性中最重要的项？

Question

I have a project object which has a list of sponsors (which is an array of Person objects) as seen below

var projectA = GetProject();
IEnumerable<Person> sponsors = projectA.Sponsors;

I now have list of these projects objects

List<Project> projects = GetProjects();

and I am trying to get the "top sponsors" for all projects

If a project had a single sponsor, I would do something like this:

var topSponsors = projects.GroupBy(r->r.Sponsor).OrderByDescending(g->g.Count)

but in my case a project has multiple sponsors so I am looking for the right syntaxt that shows the top sponsors across this list of projects?

As an example, lets say

Project 1 ==> Sponsors (Tim, Joe)
Project 2 ==> Sponsors (Tim)
Project 3 ==> Sponsors (Bill)
Project 4 ==> Sponsors (Tim, Joe)

I would want to order by:

Tim (3 projects)
Joe (2 projects)
Bill (1 projects)

Answer 1

So you want the top n persons of all persons in the projects?

var top10Persons = projects
    .SelectMany(p=> p.Sponsors)
    .GroupBy(p => p)
    .OrderByDescending(g => g.Count())
    .Take(10)
    .Select(g => g.First());

This presumes that Person overrides Equals + GetHashCode . You could also provide a custom IEqualityComparer<Peerson> for GroupBy. If you also want the Count of each person you could select an anonymos type:

    .....
    .Take(10)
    .Select(g => new { Count = g.Count(), Person = g.First() });

Answer 2

This should do the trick:

var bestSponsors = projects.SelectMany(p => p.Sponsors)
    .GroupBy(p => p.Name)
    .OrderByDescending(g => g.ToList().Count)
    .Select(p => new
           {
               Name = p.Key,
               SponsoredProjectCount = p.ToList().Count
           })
    .ToList();

I am assuming you have a person class like this:

public class Person
{
    public string Name { get; set; }
}