def links_group_by(attribute, linkz = links)
      linkz.map      { |link| { key: link.send(attribute), link: link } }
           .group_by { |entry| entry[:key] }
           .each     { |key, link| link.map! { |l| l[:link] }}
    end
def links_group_by(attribute, linkz = links)
      linkz.map      { |link| { key: link.send(attribute), link: link } }
           .group_by { |entry| entry[:key] }
           .each     { |key, link| link.map! { |l| l[:link] }}
    end
Groups the links on the provided attribute. If no links array is provided
 the links from self are used