title: column names setup after group by the data in python
body: <p><strong>My table is as bellowed</strong></p>
  <pre><code>datetime    source  Day area    Town    County  Country
  0   2019-01-01 16:22:46 1273    Tuesday Brighton    Brighton    East Sussex England
  1   2019-01-02 09:33:29 1823    Wednesday   Taunton Taunton Somerset    England
  2   2019-01-02 09:44:46 1977    Wednesday   Pontefract  Pontefract  West Yorkshire  England
  3   2019-01-02 10:01:42 1983    Wednesday   Isle of Wight   NaN NaN NaN
  4   2019-01-02 12:03:13 1304    Wednesday   Dover   Dover   Kent    England
  </code></pre>
  <p>My codes are</p>
  <pre><code>counts_by_counties = call_by_counties.groupby(['County','Town']).count()
  counts_by_counties.head()
  </code></pre>
  <p>My grouped result (Do the column name disappeared?)</p>
  <pre><code>                            datetime    source  Day    area  Country
  County            Town                  
  Aberdeenshire   Aberdeen            8       8      8    8       8
                  Banchory            1       1      1    1       1
                  Blackburn          18      18     18   18      18
                  Ellon               6       6      6    6       6
                  Fraserburgh         2       2      2    2       2
  </code></pre>
  <p><strong>I used this codes to rename the column, I am wondering if there is other efficent way to change the column name.</strong></p>
  <pre><code># slicing of  the table 
  counts_by_counties = counts_by_counties[['datetime',]]
  # rename by datetime into Counts
  counts_by_counties.rename(columns={'datetime': 'Counts'})
  </code></pre>
  <p><strong>Expected result</strong></p>
  <pre><code>                            Counts
  County            Town  
  Aberdeenshire   Aberdeen    8
                  Banchory    1
                  Blackburn   18
  </code></pre>