LINQ：从第一个项目以外的每个组中选择全部

Question

It is easy to select the first of each group:

        var firstOfEachGroup = dbContext.Measurements
            .OrderByDescending(m => m.MeasurementId)
            .GroupBy(m => new { m.SomeColumn })
            .Where(g => g.Count() > 1)
            .Select(g => g.First());

But...
Question : how can I select all from each group except the first item?

        var everythingButFirstOfEachGroup = dbContext.Measurements
            .OrderByDescending(m => m.MeasurementId)
            .GroupBy(m => new { m.SomeColumn })
            .Where(g => g.Count() > 1)
            .Select( ...? );

Additional information:
My real goal is to delete all duplicates except the last (in a bulk way, ie: not using an in-memory foreach), so after the previous query I want to use RemoveRange :

 dbContext.Measurements.RemoveRange(everythingButFirstOfEachGroup);

So, if my question has no sense, this information might be handy.

Answer 1

Use Skip(1) to skip the first record and select the rest.

Something like:

var firstOfEachGroup = dbContext.Measurements
                    .OrderByDescending(m => m.MeasurementId)
                    .GroupBy(m => new { m.SomeColumn })
                    .Where(g => g.Count() > 1)
                    .SelectMany(g => g.OrderByDescending(r => r.SomeColumn).Skip(1));

See: Enumerable.Skip

If you do not need a flattened collection then replace SelectMany with Select in code snippet.

Answer 2

IGrouping<K, V> implements IEnumerable<V> ; you simply need to skip inside the select clause to apply it to each group:

.Select(g => g.Skip(1))

Answer 3

You can always use .Distinct() to remove duplicates; presumably sorting or reverse-sorting and then applying .distinct() would give you what you want.