title: Editing the date in pandas to show year only, by column
body: <p>I am trying to understand how I can edit the dataframe in python using pandas so I can drop everything but the year. </p>
  
  <p>Example: if the date is 2014-01-01, I want it to show 2014 and drop both the month and the date. All the dates are in a single column.</p>
  
  <p>Thanks in advice!</p>