title: Simple pandas pivot table issue
body: <p>I have a dataframe like below:</p>
  
  <pre><code>+-------+--------+----------+---------------+
  |       | ios_id | video_id | feed_position |
  +-------+--------+----------+---------------+
  | 11995 | user1  |      199 |             7 |
  | 11996 | user2  |      164 |            18 |
  | 11997 | user3  |      209 |             1 |
  | 11998 | user3  |       85 |             4 |
  | 11999 | user3  |       45 |             6 |
  | 12000 | user3  |      150 |            10 |
  | 12001 | user3  |      207 |            12 |
  | 12002 | user3  |      203 |            26 |
  | 12003 | user4  |      209 |             1 |
  | 12004 | user4  |      202 |             1 |
  | 12005 | user4  |      204 |             1 |
  | 12006 | user4  |      126 |             2 |
  | 12007 | user4  |       72 |             5 |
  | 12008 | user4  |      108 |            10 |
  | 12009 | user4  |       85 |            11 |
  </code></pre>
  
  <p>What I would like to do is create a pivot table that counts the instances of each ios_id for each video_id and feed_position.  It would look like this:</p>
  
  <pre><code>+------------+---+---+---+---+---+---+----+----+----+----+----+
  | Row Labels | 1 | 2 | 4 | 5 | 6 | 7 | 10 | 11 | 12 | 18 | 26 |
  +------------+---+---+---+---+---+---+----+----+----+----+----+
  |         45 |   |   |   |   | 1 |   |    |    |    |    |    |
  |         72 |   |   |   | 1 |   |   |    |    |    |    |    |
  |         85 |   |   | 1 |   |   |   |    |  1 |    |    |    |
  |        108 |   |   |   |   |   |   |  1 |    |    |    |    |
  |        126 |   | 1 |   |   |   |   |    |    |    |    |    |
  |        150 |   |   |   |   |   |   |  1 |    |    |    |    |
  |        164 |   |   |   |   |   |   |    |    |    |  1 |    |
  |        199 |   |   |   |   |   | 1 |    |    |    |    |    |
  |        202 | 1 |   |   |   |   |   |    |    |    |    |    |
  |        203 |   |   |   |   |   |   |    |    |    |    |  1 |
  |        204 | 1 |   |   |   |   |   |    |    |    |    |    |
  |        207 |   |   |   |   |   |   |    |    |  1 |    |    |
  |        209 | 2 |   |   |   |   |   |    |    |    |    |    |
  +------------+---+---+---+---+---+---+----+----+----+----+----+
  </code></pre>
  
  <p>I tried:</p>
  
  <pre><code>pd.pivot_table(df, values=['ios_id'],
                 index=['video_id'], columns=['video_id',
                 'feed_position'], aggfunc=np.count_nonzero)
  </code></pre>
  
  <p>But I was met with this error: <code>KeyError: 'Level video_id not found'</code></p>
  
  <p>Any thoughts on how I can accomplish this?</p>