What would be the Linq code for this grouping using VB.NET 2008?

I have a population aged from 0 to 119 years.

I wish to group this开发者_开发百科 population from the age of 15 to 49 according to the following hypothesis:

1. 15 to 19;
2. 20 to 24;
3. 25 to 29;
4. 30 to 34;
5. 35 to 39;
6. 40 to 44;
7. 45 to 49.

Any age apart these are useless for the calculation I need to perform. Here are some sample data and code.

I have an AnnualPopulation class which represents the demographic population for each year of age.

Public Class AnnualPopulation
    Public Id as Integer
    Public Year As Integer
    Public Gender As String
    Public YearsOfAge As Double?() = New Double?(119) { }
End Class

Then, the YearsOfAge array/collection property contains the number of people based on their gender. For instance:

AnnualPopulation.Year = 2009
AnnualPopulation.Gender = "F"c
For age As Integer = 0 To AnnualPopulation.YearsOfAge.Length - 1 Step 1
    YearsOfAge(age) = 42356.67F 'Of course, this number varies from a years of age to another!'
Next

I would then like to group such as follows:

Dim groups() As Double = New Double(6) { }
For age As Integer = 15 To 49 Step 1
    Dim index As Integer = 0

    Select Case age
        Case 15 to 19
            index = 0
        Case 20 To 24
            index = 1
        Case 25 To 29
            index = 2
        Case 30 To 34
            index = 3
        Case 35 To 39
            index = 4
        Case 40 To 44
            index = 5
        Case 45 To 49
            index = 6
    End Select

    groups(index) += AnnualPopulation.YearsOfAge(age - 1)
Next

This way, I would have the sum of population for each range of year of age

So, I though of grouping them, and then I have no common key to group them by, no luck! =P In C#, I guess this would do what I need:

double[] groups = new double[7];
Enumerable.Range(15, 34).ToList().ForEach(age => {
    groups[(int)(age % 4)] += annualPopulation.YearsOfAge[age - 1].HasValue 
                              ? annualPopulation.YearsOfAge[age - 1].Value : 0.0;
});

Which I don't seem to be able to achieve in VB.NET 2008 except if I try to go along with New Action(Of T1, T2) or else Func(Of Double?, TKey). I'm not comfortable at all with these! =( (Underlying question: Why is it so complicated in VB.NET to work with lambdas!?)

My code actually works, I'm only looking for a nicer and perhaps more readable solution, though this is easy to understand what I'm trying to achieve here.

Anyway, anyone has a clue about how to go with this?

Thanks in advance! =)

Use your switch statement in the group by selector; the keys will be 0 to 6 respectively then. After that, you simply can use the Sum operator on each group.

In C#, it would look like this (you don't have ranged cases in C#):

var filtered = data
    .Where(item => item.Age > 15 && item.Age <= 49)
    .GroupBy(item => 
                    {
                     if(item.Age > 15 && item.Age <= 19)
                       return 0;
                     else if(item.Age <= 24)
                       return 1;
                     else if(item.Age <= 29)
                       return 2;
                     else if(item.Age <= 34)
                       return 3;
                     else if(item.Age <= 39)
                       return 4;
                     else if(item.Age <= 44)
                       return 5;
                     else if(item.Age <= 49)
                       return 6;
                    });

After that, you can create a dictionary:

var dict = filtered.ToDictionary(i => i.Key, i => /* do something with the sequence */);