"Grouping" dictionary by value

Question

I have a dictionary: Dictionary<int,int>. I want to get new dictionary where keys of original dictionary represent as List<int>. This is what I mean:

var prices = new Dictionary<int,int>();

The prices contain the following data:

1   100
2   200
3   100
4   300

I want to get the IList<Dictionary<int,List<int>>>:

int      List<int>
100      1,3
200      2
300      4

How can I do this?

Answer 1

You can use GroupBy.

Dictionary<int,List<int>> groups = 
             prices.GroupBy(x => x.Value)
                   .ToDictionary(x => x.Key, x => x.Select(i => i.Key).ToList());