Group by, sum and find top 10

Check out 101 LINQ Samples[^] from Microsoft.
Through this you should be able to find the right LINQ phrase.

But perhaps something like this can give you a start?

// Make the group first.
var groups = from row in rows
             group row by row.Column1 into g
             select new { GroupKey = g.Key, Value = g };

// Get top 10
var results = (from g in groups
               order by g.Value.Column2
               select g.Value).Take(10);

// look at the results
foreach (var result in results)
{
  var name = result.Column2;
}