title: Pandas Category sub-group 0 counts
body: <p>I'm new to Pandas, and trying to generate a table of subgroup counts maintaining the category order, and showing zero counts. It's a simple category with 4 options. </p>
  
  <p>Without grouping it works as expected, but with grouping it isn't displaying zero counts (see last group). </p>
  
  <p>In [21]:</p>
  
  <pre><code>df2['Call_cat'] = df2['Group_INV'].astype('category')
  counts = df2['Call_cat'].value_counts(dropna=True, sort=False)
  counts
  </code></pre>
  
  <p>Out[21]:</p>
  
  <pre><code>1.0    35773
  2.0      290
  3.0     8680
  4.0    18867
  Name: Call_cat, dtype: int64
  </code></pre>
  
  <p>In [22]:</p>
  
  <p>grouped = df2.groupby('Z1')['Call_cat'].value_counts(dropna=True, sort=False)
  grouped</p>
  
  <p>Out[22]:</p>
  
  <pre><code>Z1    Call_cat
  ZLZO  1.0         2961
        2.0           24
        3.0          476
        4.0         1221
  ZZRE  1.0          307
        2.0            2
        3.0          152
        4.0          197
  ZZMB  1.0          904
        3.0          198
        4.0          906
  </code></pre>