Dynamic Group By clause in linq query - asp.net

Question

The following linq query groups people in a city by their professions.
However the only way I've been able to get it to work is to hardcode the cities.
Each Person has a City. How can I modify the below query so that it groups by all the distinct cities that are returned in my query?
profession = people
.GroupBy(p => p.Profession).
Select(group =>
new
{
name = group.Key,
data =
new List<int>()
{
group.Count(p => p.City == "Adelaide"),
group.Count(p => p.City == "Brisbane"),
group.Count(p => p.City == "Canberra"),
group.Count(p => p.City == "Darwin"),
group.Count(p => p.City == "Melbourne"),
group.Count(p => p.City == "Perth"),
group.Count(p => p.City == "Sydney"),
},
})
Ie, if my data set was:
Person {id:1, city: "Paris" }
Person {id:2, city: "Paris" }
Person {id:3, city: "London" }
Then the resulting query would be:
profession = people
.GroupBy(p => p.Profession).
Select(group =>
new
{
name = group.Key,
data =
new List<int>()
{
group.Count(p => p.City == "Paris"),
group.Count(p => p.City == "London"),
},
})

Answer 1

This yields the same output as your hardcoded list, but I'm not sure if it's what you want (hint: giving us your expected output will help a lot in that regard).
It simply creates a distinct list of the cities, then builds a predicate delegate that counts the occurrence of each city, and adds that predicate to a list. When the actual grouping is performed, each predicate in the list is invoked with the result of the grouping.
The notation Func<IGrouping<string, Person>, int> simply says "this is a delegate that takes an IGrouping<string, Person> object (the result of calling GroupBy) and returns an int (the result of calling Count)".
class Program
{
static void Main(string[] args)
{
var people = new List<Person>()
{
new Person(1, "Paris", "carpenter"),
new Person(2, "Paris", "bricklayer"),
new Person(3, "London", "video game critic"),
};
var distinctCities = people.Select(p => p.City).Distinct();
var groupPredicates = new List<Func<IGrouping<string, Person>, int>>();
foreach (var city in distinctCities)
{
groupPredicates.Add(g => g.Count(p => p.City == city));
}
var professions = people
.GroupBy(p => p.Profession)
.Select(g =>
new
{
name = g.Key,
data = groupPredicates.Select(gp => gp(g)),
});
foreach (var profession in professions)
{
Console.WriteLine(profession.name + " =>");
foreach (var count in profession.data)
{
Console.WriteLine(" " + count);
}
}
Console.ReadKey(true);
}
}
struct Person
{
public int Id { get; set; }
public string City { get; set; }
public string Profession { get; set; }
public Person(int id, string city, string profession)
{
Id = id;
City = city;
Profession = profession;
}
}