You're right, but it's not just `filter`. Any command that can run on a group can run on a full table and vice versa. For example:

  # get a sample of 3 elements from a table
  r.table('foo').sample(3)
  
  # get a sample of 3 elements from each group
  r.table('foo').group('category').sample(3)

You could say that we created two versions of `filter`, and `sample`, and every other command. But another way to say it is that we use polymorphism, which is widely considered an advantage in modern programming languages.

Yeah, it's definitely more expressive and terse I just don't think your argument against WHERE/HAVING is incredibly strong. Someone could also just do subqueries and only use WHERE and achieve the exact same behavior that you offer (albeit with a ton more typing).

HAVING exists because it was created prior to subqueries/dynamic tables, otherwise we'd have been likely to just use:

    select * from (select category, sum(num_comments) as comments from posts group by category) as temp where comments > 7

As a LINQ user, I expected group('category').sample(3) to sample 3 categories, not to sample inside each category.

In ReQL you can do it with group('category').ungroup().sample(3). It's really powerful once you get the hang of it.