GroupBy a Dictionary based on key

Question

I have a Dictionary<string,string> that I want to group. Here are some sample key/value pairs

==========================
| Key            | Value |
==========================
| A_FirstValue   | 1     |
| A_SecondValue  | 2     |
| B_FirstValue   | 1     |
| B_SecondValue  | 2     |
==========================

Now, I want to group it according to the first letter or word in the key before the first instance of the character '_'

So, the final result will be Dictionary<string, Dictionary<string, string>>. For the example above the result will be:

A -> A_FirstValue, 1
     A_SecondValue, 2

B -> B_FirstValue, 1
     B_SecondValue, 2

Is this even possible? Anyone who could help me please?

Thanks.

Answer 1

Well, you could use:

var dictionary = dictionary.GroupBy(pair => pair.Key.Substring(0, 1))
       .ToDictionary(group => group.Key,
                     group => group.ToDictionary(pair => pair.Key,
                                                 pair => pair.Value));

The group part will give you an IGrouping<string, KeyValuePair<string, string>>, and the subsequent ToDictionary will convert each group of key/value pairs back into a dictionary.

EDIT: Note that this will always use the first letter. For anything more complicated, I would probably write a separate ExtractFirstWord(string) method and call that in the GroupBy lambda expression.