How keys are reorganized after C# LINQ convert a dictionary to a query?

Question

I am working on C# converting a dictionary to query :

public class myClass
{
    public int my_id;
    public Dictionary<string, Dictionary<string, string[]>> myDict;
}

Dictionary<string, myClass> dataDict;


var queryDict = (from happen in dataDict
        group happen by happen.Value.my_id into g select g)
       .ToDictionary(g => g.Key, g => g.ToDictionary(x => x.Key, x => x.Value));

I need to iterate every element of queryDict.

Before doing the query, for the same dataDict's key, there may be multiple myClass that have the same event_id.

After query, for the same happen.Value.my_id, how the dataDict' s original keys are organized ? They are a list pointed by the one event_id ?

Any help would be appreciated !

Answer 1

Basically group by gives you an IGrouping<TKey, TElement> which is an IEnumerable<TElement> ( IGrouping Interface ), so having this query:

from happen in dataDict group happen by happen.Value.my_id into g select g

means, you group by happen.Value.my_id , so the TKey will be my_id and the TElement would be a KeyValuePair<string, MyClass>> which is the items of your dictionary. Since the IGrouping<int, KeyValuePait<stirng, MyClass>> which is the result of above query is actually an IEnumerable<keyValuePair<string, MyClass>> , so for every key you actually have an IEnumerable<KeyValuePair<string, MyClass>> . As you can see here, you have the elements of you dictionary as they were. Second part of the query is just converting the IEnumerable<IGrouping<int, Dictionary<string, MyClass>>> to a Dictionary<int, Dictionary<string, MyClass>>> so it's not big deal.

Answer 2

Effectively, your dataDict is an array of KeyValuePair (1-dimensonal array). And your query adds another dimension, so it becomes a Dictionary of Dictionaries . But adding another dimension is just a grouping of older elements by a new key.

It's better to illustrate it like this: