title: Is this the correct method for changing dates in Pandas/Python?
body: <p>I have a csv file with a "Date Joined" column in the form : "January 5, 2015"
  I want to convert to "2015-01-05"</p>
  
  <p>Here is what I have done with pandas : </p>
  
  <pre><code>for i in range(len(data)):
      dt_obj = dt.datetime.strptime(data["Date Joined"][i] , "%B %d, %Y")
      result = dt_obj.strftime("%Y-%m-%d")
      data["Date Joined"][i] = result
  </code></pre>
  
  <p>This works, but I have a feeling this is not really correct and very slow.</p>
  
  <p>Is this the correct method ? Should I proceed differently ?</p>
  
  <p>Thanks.</p>