Group by in LINQ

Question

Let\'s suppose if we have a class like:

class Person { 
    internal int PersonID; 
    internal string car; 
}

I have a list of this class

Answer 1

Try this :

var results= persons.GroupBy(n => n.PersonId)
            .Select(g => new {
                           PersonId=g.Key,
                           Cars=g.Select(p=>p.car).ToList())}).ToList();

But performance-wise the following practice is better and more optimized in memory usage (when our array contains much more items like millions):

var carDic=new Dictionary>();
for(int i=0;i(){person.car};
   }
}
//returns the list of cars for PersonId 1
var carList=carDic[1];