title: Bundle columns of a DataFrame into hierarchical index
body: <p>If I have preexisting columns (say 12 columns, all with unique names), and I want to organize them into two &quot;header&quot; columns, such as 8 assigned to <code>Detail</code> and 4 assigned to <code>Summary</code>, what is the most effective approach besides sorting them, manually creating a new index, and then swapping out the indices?</p>
  <p>Happy to provide more example detail, but that's the gist of what is pretty generic problem.</p>