GroupBy

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Example

var persons = new[] {
    new { Name="Fizz", Job="Developer"},
    new { Name="Buzz", Job="Developer"},
    new { Name="Foo", Job="Astronaut"},
    new { Name="Bar", Job="Astronaut"},
};

var groupedByJob = persons.GroupBy(p => p.Job);

foreach(var theGroup in groupedByJob)
{
    Console.WriteLine(
        "{0} are {1}s", 
        string.Join(",", theGroup.Select(g => g.Name).ToArray()),
        theGroup.Key);
}

//Fizz,Buzz are Developers
//Foo,Bar are Astronauts

Group invoices by country, generating a new object with the number of record, total paid, and average paid

var a = db.Invoices.GroupBy(i => i.Country)
          .Select(g => new { Country = g.Key,
                             Count = g.Count(),
                             Total = g.Sum(i => i.Paid),
                             Average = g.Average(i => i.Paid) });

If we want only the totals, no group

var a = db.Invoices.GroupBy(i => 1)
          .Select(g => new { Count = g.Count(),
                             Total = g.Sum(i => i.Paid),
                             Average = g.Average(i => i.Paid) });

If we need several counts

var a = db.Invoices.GroupBy(g => 1)
          .Select(g => new { High = g.Count(i => i.Paid >= 1000),
                             Low = g.Count(i => i.Paid < 1000),
                             Sum = g.Sum(i => i.Paid) });

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Contributors: 2
2016-07-22
Licensed under: CC-BY-SA

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