Question

I want to filter the objects that I have by their topic.

I have many topics: Arts, Economics, Business, Politics. Each topic is a property within the object that I try to classify from a list of those objects.

Here is part of my objects:

public class AllQuestionsPresented
{
    public string Name{ get; set; }
    public string ThreadName { get; set; }
    public string Topic { get; set; }
    public string Subtopic { get; set; }
    public int Views { get; set; }
    public int Replies { get; set; }
    public int PageNumber { get; set; }
    public DateTime Time { get; set; }
    // snip

I created many of those objects feed their properties with different values and put them into a List:

List<AllQuestionsPresented> forumData;

Now I want to group them all into linq by their topics..

var groupedByPages =
    from n in forumData
    group n by forumData
    select .....

Basically i dont know how to continue cause i am not used to deal with linq.. what i want to get is some dictionary..

Dictionary<string,AllQuestionsPresented> dictionary..

If i dont use linq, and add to a dictionary every topic, it will put several “AllQuestionsPresented” objects with the same topic..which will throw an exception..so i have to use group by..but dont know how to achieve that manipulation

Answer 1

You can just call ToDictionary. The parameters are a function to select the keys and another to select the values:

var groupedByPages =
    from n in forumData
    group n by n.Topic;

IDictionary<string, IEnumerable<AllQuestionsPresented>> dictionary = 
    groupedByPages.ToDictionary(x => x.Key, x => x.AsEnumerable());

But if all you need from the IDictionary interface is the indexing operation, it’s easier to just use a ILookup:

ILookup<string, AllQuestionsPresented> groupedByPages = forumData.ToLookup(x => x.Topic);