title: Keep empty bins/buckets in final GroupBy even if there is no data to populate them
body: <p>I have successfully bucketted my data:</p>
  
  <pre><code>bins = [-np.inf,0,10000,20000,40000,60000,80000,100000,np.inf]  # include infinity value as the endpoint to the bins
  labels = ['0','10K', '20K','40K','60K', '80K','100K','&gt; 100K']
  df_Done = df[
                  (df['state'].str.contains('Done'))
                  ][['Year_Month','rfq_qty_CAD_Equiv']].copy()
  display(df_Done.head(5))
  
  Year_Month  rfq_qty_CAD_Equiv
  2018-05     259,774
  2018-05     259,774
  2018-05     363,684
  2018-05     3,896,610
  2018-05     666,340
  
  df_Done.info()
  Year_Month           700 non-null object
  rfq_qty_CAD_Equiv    700 non-null float64
  Bucket               700 non-null category
  
  df_Done['Bucket'] = pd.cut(df_Done['rfq_qty_CAD_Equiv'], bins=bins, labels=labels)
  display(df_Done.groupby(['Year_Month','Bucket'], as_index=False)['Bucket'].size())
  </code></pre>
  
  <p>From month to month some buckets may have no trades, in which case I would like the bucket line to appear with a zero. Example in the result below, there is no 10K bucket for 2017-11 (want to see 10K and a 0). Is there a way to insert the bins/buckets even if there are no trades there to populate these buckets? </p>
  
  <p>Also is there a way to ouput the result not in text format but in grid format?  </p>
  
  <p><a href="https://i.stack.imgur.com/8g8JD.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/8g8JD.png" alt="enter image description here"></a></p>