title: Fastest way to multiply multiple columns in Dataframe based on conditions
body: <pre><code>data = [{'a': 12, 'b': 23, 'c':34, 'd': 0.1, 'e':25},
          {'a':13, 'b': 26, 'c': 38, 'd': 0.02, 'e':26},
          {'a':19, 'b': 28, 'c': 31, 'd': 0.04, 'e':22}
         ]
   
  # Creates DataFrame.
  df = pd.DataFrame(data)
  </code></pre>
  <pre><code>     a   b   c    d     e
  0   12  23  34  0.10    25
  1   13  26  38  0.02    26
  2   19  28  31  0.04    22
  </code></pre>
  <p>I have a very large dataframe consisting of 20 cols and 20million+ rows, I would like to multiply certain columns by column d.</p>
  <p>For example in this case I want to multiply columns a,c, and e by the percentage in column d.I would like to know what is the quickest way to do this</p>