Linq query to get a duplicate key once along with multiple values out of a dictionary

Question

I have the following dictionary:

Dictionary<int, string> selectedDrivers = new Dictionary<int, string>()
{
    { 1, "Michael Schumacher" },
    { 2, "Michael Schumacher" },
    { 3, "Jensen Button" }
};

What I try to achieve is a linq query that will find the duplicates, retrieve the name only once, along with the positions this duplicate has. So, for example, the above would result in "Michael Schumacher" 1 2. I would like the result to go into a Dictionary<string, List<int>>.

Getting excited fast, this little nugget I wrote seems to be going in the right direction, except that I have Michael Schumacher twice. And it's not yet in a Dictionary<string, List<int>>

var a = selectedDrivers.GroupBy(a => a.Value).
        Where(b => b.Count() > 1);

You can't do that in only one Linq request I think

Arnaud F.
– Arnaud F.

2011-06-29 19:44:55 +00:00
Commented Jun 29, 2011 at 19:44 — Arnaud F.
– Arnaud F., Commented Jun 29, 2011 at 19:44

Mo Valipour · Accepted Answer · 2011-06-29 19:59:03Z

3

var a = selectedDrivers.GroupBy(a=>a.Value)
            .Where(g=>g.Count() > 1)
            .ToDictionary(g => g.Key, g => g.Select(a=>a.Key).ToList());

answered Jun 29, 2011 at 19:59

Mo Valipour

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