7.times { @doctor.schedules.build }

<tr>
    <% @i = 0 %>
    <%= f.simple_fields_for :schedules do |builder| %>
    <td>
    <%= builder.input :day, value: @y, wrapper: :check  %>
    <%= builder.input :is_available, as: :boolean, label: false, wrapper: :check %>
    <% @i += 1 %>
    </td>
<% end %>
</tr>

<% @doctor.schedules.each_with_index do |schedule, index| %>
  <%= f.simple_fields_for :schedules, schedule do |ff| %>
    <%= ff.input :day, value: index %>
  <% end %>
<% end %>

<%= f.simple_fields_for :schedules do |builder| %>
  <%= builder.input :day, value: builder.index+1 %>
<% end %>