collecting render calls from helper method

render_loop_in_helper.rb

  def account_tree(root, partial, output="")
    sorter = ->(n) {[n.content.index_path, n.content.number]}
    output += render(partial: partial, object: root.content) if root.content
    root.children.sort_by(&sorter).each {|node| output = account_tree(node, partial, output)}
    output.html_safe
  end