title: Splitting a Column on Positive and Negative values
body: <p>How do you split a column into two different columns based on a criteria, but maintain one key? For example</p>
  
  <pre><code>      col1  col2   time       value
  0      A     sdf  16:00:00     100
  1      B     sdh  17:00:00     -40
  2      A     sf   18:00:45     300 
  3      D     sfd  20:04:33     -89
  </code></pre>
  
  <p>I want a new dataframe like this</p>
  
  <pre><code>     time       main_val    sub_val
  0   16:00:00     100         NaN
  1   17:00:00     NaN         -40
  2   18:00:45     300         NaN
  3   20:04:33     NaN         -89
  </code></pre>