title: Add new column containing an Array of column names sorted by the row-wise values
body: <p>Given a dataFrame with a few columns, I'm trying to create a new column containing an array of these columns' names sorted by decreasing order, based on the row-wise values of these columns.</p>
  
  <pre><code>| a | b | c | newcol|
  |---|---|---|-------|
  | 1 | 4 | 3 |[b,c,a]|
  | 4 | 1 | 3 |[a,c,b]|
  ---------------------
  </code></pre>
  
  <p>The names of the columns are stored in a var names:Array[String]</p>
  
  <p>What approach should I go for?</p>