_filter-links.html.erb (partial)

<ul class="organiser__group organiser__group--sort">
   <%= content_tag(:li, class: ("active" if params[:sort] == "park" || params[:sort] == nil)) do %>
      <%= link_to "By Park", coasters_path(sort_parameters(:park, page: 1)), remote: true %>
   <% end %>

   <%= content_tag(:li, class: ("active" if params[:sort] == "alphabetically")) do %>
      <%= link_to "Alphabetically", coasters_path(sort_parameters(:alphabetically, page: 1)), remote: true %></li>
   <% end %>

   <%= content_tag(:li, class: ("active" if params[:sort] == "order")) do %>
      <%= link_to "Order ridden", coasters_path(sort_parameters(:order, page: 1)), remote: true %>
   <% end %>
</ul>

<ul class="organiser__group organiser__group--filter">
   <%= content_tag(:li, class: ("active" if params[:type] == "steel")) do %>
      <%= link_to "Steel", coasters_path(type_parameters("steel", page: 1)), remote: true %>
   <% end %>

   <%= content_tag(:li, class: ("active" if params[:type] == "wood")) do %>
      <%= link_to "Wood", coasters_path(type_parameters("wood", page: 1)), remote: true %>
   <% end %>

   <%= content_tag(:li, class: ("active" if params[:type] == "powered")) do %>
      <%= link_to "Powered", coasters_path(type_parameters("powered", page: 1)), remote: true %>
   <% end %>
</ul>

<ul class="organiser__group organiser__group--filter">
   <%= content_tag(:li, class: ("active" if params[:letters] == "#")) do %>
      <%= link_to "#", coasters_path(letter_parameters("#", page: 1)), remote: true %>
   <% end %>

   <%= content_tag(:li, class: ("active" if params[:letters] == "a-e")) do %>
      <%= link_to "A-E", coasters_path(letter_parameters("a-e", page: 1)), remote: true %>
   <% end %>

   <%= content_tag(:li, class: ("active" if params[:letters] == "f-j")) do %>
      <%= link_to "F-J", coasters_path(letter_parameters("f-j", page: 1)), remote: true %>
   <% end %>

   <%= content_tag(:li, class: ("active" if params[:letters] == "k-o")) do %>
      <%= link_to "K-O", coasters_path(letter_parameters("k-o", page: 1)), remote: true %>
   <% end %>

   <%= content_tag(:li, class: ("active" if params[:letters] == "p-t")) do %>
      <%= link_to "P-T", coasters_path(letter_parameters("p-t", page: 1)), remote: true %>
   <% end %>

   <%= content_tag(:li, class: ("active" if params[:letters] == "u-z")) do %>
      <%= link_to "U-Z", coasters_path(letter_parameters("u-z", page: 1)), remote: true %>
   <% end %>
</ul>

<ul class="organiser__group organiser__group--filter">
   <%= content_tag(:li, class: ("active" if params[:misc] == "milestones")) do %>
      <%= link_to "Milestones", coasters_path(misc_parameters("milestones", page: 1)), remote: true %>
   <% end %>
</ul>

coaster_helper.rb

module CoasterHelper

  # Add the type parameter to URL if not already there and remove if they are
  def type_parameters(type, options = {})
    parameters = params.dup

    if params[:type] == type
      # Remove type
      parameters.delete(:type)
    else
      # Add type to new parameters variable
      parameters.merge!(type: type)
    end

    # Merge any parameters passed in via options
    parameters.merge(options)
  end


  # Add the letters parameter to URL if not already there and remove if they are
  def letter_parameters(letters, options = {})
    parameters = params.dup

    if params[:letters] == letters
      # Remove letters
      parameters.delete(:letters)
    else
      # Add letters to new parameters variable
      parameters.merge!(letters: letters)
    end

    # Merge any parameters passed in via options
    parameters.merge(options)
  end


  # Add the misc parameter to URL if not already there and remove if they are
  def misc_parameters(misc, options = {})
    parameters = params.dup

    if params[:misc] == misc
      # Remove misc
      parameters.delete(:misc)
    else
      # Add misc to new parameters variable
      parameters.merge!(misc: misc)
    end

    # Merge any parameters passed in via options
    parameters.merge(options)
  end


  # Add the sort parameter to URL
  def sort_parameters(sort, options = {})
    parameters = params.dup

   # Add sort to new parameters variable
   parameters.merge!(sort: sort)

    # Merge any parameters passed in via options
    parameters.merge(options)
  end

end

coasters_controller.rb (partial)

if params[:letters] || params[:type] || params[:misc] || params[:country]
         @coasters = Coaster.uniques

         if params[:type]
            filter_by_type

            # Determine order based on whether 'letters' parameter is present
            if params[:letters]
               # Order by coaster name
               params[:sort] = 'alphabetically' unless params[:sort]
            else
               # Order by park name then coaster name
               params[:sort] = 'park' unless params[:sort]
            end
         end

         if params[:letters]
            filter_by_letters

            # Determine order based on whether 'type' parameter is present
            if params[:type]
               # Order by park name then coaster name
               params[:sort] = 'park' unless params[:sort]
            else
               # Order by coaster name
               params[:sort] = 'alphabetically' unless params[:sort]
            end
         end

         if params[:misc]
            filter_by_misc
         end

         if params[:country]
            filter_by_country
         end

      else
         @coasters = Coaster.uniques
      end

      if params[:sort] == 'order'
         @coasters = @coasters.except(:order).order('coasters.order_ridden ASC')
      elsif params[:sort] == 'park'
         @coasters = @coasters.joins(:park).order('parks.name ASC').order('coasters.name ASC')
      elsif params[:sort] == 'alphabetically'
         @coasters = @coasters.except(:order).order('coasters.name ASC')
      else
         @coasters = @coasters.joins(:park).order('coasters.name ASC').order('parks.name ASC')
      end