title: Drop percentage of a dataframe [pandas]
body: <p>I have a dataset with a very long tail and wish to sample only 90% of the data.</p>
  
  <pre><code>city          score
  bangkok       60
  kl            20
  sydney        10
  melbourne     5
  dhaka         5
  </code></pre>
  
  <p>should be:</p>
  
  <pre><code>city          score
  bangkok       60
  kl            20
  sydney        10
  </code></pre>