Linq groupby return unique group

I have list of records, each record has Name and Rounds. Rounds is a concatenated numbers seperated by "-"

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How can i group by name and display only unique rounds, also count the number of rounds and display the first round and last round

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Here is what i tried, 

 data.GroupBy(d => d.Name)
.Select(
    g => new
    {
        Name = g.Key,
        Rounds = g.Concat(s => s.Rounds),
        NumberOfRounds =  g.Concat(s => s.Rounds).Split('-').Count,
        FirstRound = //??,
        LastRound = //??,
    });
Jon Skeet
people
quotationmark

I would start by projecting your entity to a name and collection-of-rounds pair. That will then be easier to work with. For example:

var query = results
    .Select(d => new { d.Name, Results = d.Rounds.Split('-').Select(int.Parse).ToList() })
    .GroupBy(
        d => d.Name, (key, values) => new {
            Name = key,
            Rounds = values.SelectMany(v => v.Rounds)
                           .Distinct()
                           .OrderBy(x => x)
                           .ToList()
       });

With the rounds available as a list, I don't see that there's much point in having NumberOfRounds, FirstRound and LastRound as properties, as you can just use Rounds.Count, Rounds.First(), Rounds.Last(). The important part is transforming the data into a more useful format as early as possible.

If you really need that in properties, it's easy enough to project:

// query as before, but with
.Select(x => new {
    x.Name,
    x.Rounds,
    NumberOfRounds = x.Rounds.Count,
    FirstRound = x.Rounds.First(),
    LastRound = x.Rounds.Last()
});

people

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