title: vectorize groupby pandas
body: <p>I have a dataframe like this:</p>
  
  <pre><code>day    time    category   count    
  
   1      1         a         13
   1      2         a         47
   1      3         a         1
   1      5         a         2
   1      6         a         4
   2      7         a         14
   2      2         a         10
   2      1         a         9
   2      4         a         2
   2      6         a         1
  </code></pre>
  
  <p>I want to group by day, and category and get a vector of the counts per time. Where time can be between 1 and 10. The max and min of time I have defined in two variables called max and min. </p>
  
  <p>This is how I want the resulting dataframe to look:</p>
  
  <pre><code>day     category   count    
  
   1          a      [13,47,1,0,2,4,0,0,0,0]
   2          a      [9,10,0,2,0,1,14,0,0,0]
  </code></pre>
  
  <p>Does anyone know how to make this aggregation into a vaector?</p>