title: Pivot Table to Dictionary
body: <p>I have this pivot table:</p>
  
  <pre><code>[in]:unit_d
  
  [out]:
                           units
  store_nbr   item_nbr    
     1            9        27396
                  28        4893
                  40        254
                  47        2409
                  51        925
                  89        157
                  93        1103
                  99        492
  
      2           5         55104
                  11        655
                  44        117125
                  85        106
                  93        653
  </code></pre>
  
  <p>I want to have a dictionary with 'store_nbr' as the key and 'item_nbr' as the values.<br>
  So, <code>{'1': [9, 28, 40,...,99], '2': [5, 11 ,44, 85, 93], ...}</code></p>