title: How to count the distinct values across a column in pandas
body: <p>i have a dataframe like:</p>
  
  <pre><code>Company Date        Country
  ABC     2017-09-17   USA
  BCD     2017-09-16   USA
  ABC     2017-09-17   USA
  BCD     2017-09-16   USA
  BCD     2017-09-16   USA
  ABC     2017-09-19   USA
  </code></pre>
  
  <p>I want to get a resultant df as :</p>
  
  <pre><code>Company  No: of distinct Days
  ABC      2
  BCD      1
  </code></pre>
  
  <p>How do i do it ?</p>