def per_page_select(collection, name=nil, value=nil, options={})
  unless collection.empty?
    per_page = collection.first.class.per_page
    name     = name || 'per_page'
    value    = value || params[:per_page] || per_page.to_s
    before   = options[:before_default] || ["#{per_page/2}"]
    after    = options[:after_default] || ["#{per_page*2}"]
    choices  = options_for_select(before + ["#{per_page}"] + after, value)
    select_tag name, choices, options
  end
end