title: Python rank: give negative rank to negative numbers
body: <p>I have a basic set of data like:</p>
  <pre><code>ID Value
  A  0.1
  B  0.2
  C  -0.1
  D  -0.01
  E  0.15
  </code></pre>
  <p>If we use data.rank() we get the result:</p>
  <pre><code>ID Value
  A  3
  B  5
  C  1
  D  2
  E  4
  </code></pre>
  <p>But i want to have so that the negative values result in an negative rank instead such as:</p>
  <pre><code>ID Value
  A  1
  B  3
  C  -2
  D  -1
  E  2
  </code></pre>
  <p>Basically rank give the negative values an negative rank while the postive values get a positive rank but instead of 1 to 5 we get 1 to 3 and -1 to -2.
  Any help is greatly apreciated.</p>