title: Remove Column name in a dictionary generated via Pandas
body: <p>I have a dataframe in Pandas with two columns 'page_id' and 'access_time'. Each page_id could have multiple access_time values
  Using the following code:</p>
  
  <pre><code>df.groupby('page_id').apply(lambda dfg: dfg.drop('page_id', 
  axis=1).to_dict(orient='list')).to_dict()
  </code></pre>
  
  <p>I got the output as a nested dictionary:</p>
  
  <pre><code>{id1: {'access_time':[time1,time2]},id2:{'access_time':[time3]}}
  </code></pre>
  
  <p>What I want is a dictionary of lists as follows:</p>
  
  <pre><code>{id1:[time1,time2],id2:[time3]...}
  </code></pre>
  
  <p>How can I do that ?</p>
  
  <p>And example of the Data is:</p>
  
  <pre><code>      page_id     accessed_time(string)
  0     01          20171223
  1     01          20171224
  2     02          20171226
  3     03          20171227
  </code></pre>