title: Select columns from DataFrame if first row is 0
body: <p>I am trying to select all columns of a dataframe(df) into a new dataframe where the value of the first row is ==0.</p>
  <p>df=</p>
  <pre><code>   a  b  c  d
  0  1  0  3  0
  1  2  7  2  2
  2  3  5  2  1
  </code></pre>
  <p>new_df:</p>
  <pre><code>     b   d
  0    0   0
  1    7   2
  2    5   1
  </code></pre>
  <p>It feels like a simple task but I am completly stuck in finding something that works. Thanks in advance!</p>