vertden

Pledge.all.to_a.group_by{|p| p.created_at.day}.map{|day,p| [day, p.size]}.inject({}) do |q,w|
  q.merge!({w[0]=>w[1]})
end

vertden

Pledge.all.to_a.group_by{|p| p.created_at.day}.map{|day,p| Hash[day, p.size] }