title: Reorder day of week in pandas groupby plot bar
body: <p>I have sorted df data like below:</p>
  
  <pre><code>                      day_name  Day_id
  time                                  
  2019-05-20 19:00:00     Monday       0
  2018-12-31 15:00:00     Monday       0
  2019-02-25 17:00:00     Monday       0
  2019-05-06 20:00:00     Monday       0
  2019-03-12 12:00:00    Tuesday       1
  2019-04-16 15:00:00    Tuesday       1
  2019-04-02 18:00:00    Tuesday       1
  2019-02-05 09:00:00    Tuesday       1
  2019-05-28 21:00:00    Tuesday       1
  2019-01-15 12:00:00    Tuesday       1
  2019-06-04 20:00:00    Tuesday       1
  2018-12-04 07:00:00    Tuesday       1
  2019-01-22 11:00:00    Tuesday       1
  2019-01-09 07:00:00  Wednesday       2
  2019-03-06 16:00:00  Wednesday       2
  2019-06-19 17:00:00  Wednesday       2
  2019-04-10 20:00:00  Wednesday       2
  2019-04-24 15:00:00  Wednesday       2
  2019-01-31 08:00:00   Thursday       3
  2019-01-03 08:00:00   Thursday       3
  2019-02-28 19:00:00   Thursday       3
  2019-05-23 20:00:00   Thursday       3
  2018-12-20 07:00:00   Thursday       3
  2019-05-09 19:00:00   Thursday       3
  2019-06-28 15:00:00     Friday       4
  2019-03-22 12:00:00     Friday       4
  2019-03-29 14:00:00     Friday       4
  2018-12-15 08:00:00   Saturday       5
  2019-02-17 11:00:00     Sunday       6
  2019-06-16 19:00:00     Sunday       6
  2018-12-02 08:00:00     Sunday       6
  </code></pre>
  
  <p>Currentry with help of this <a href="https://stackoverflow.com/questions/27365467/can-pandas-plot-a-histogram-of-dates">post</a>:</p>
  
  <pre><code>df = df.groupby(df.day_name).count().plot(kind="bar")
  plt.show()
  </code></pre>
  
  <p>my output is:</p>
  
  <p><a href="https://i.stack.imgur.com/InXvv.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/InXvv.png" alt="enter image description here"></a></p>
  
  <p>How to plot histogram with days of week in proper order like: Monday, Tuesday ...?</p>
  
  <p>I have found several approaches: <a href="https://stackoverflow.com/questions/22635110/sorting-the-order-of-bars-in-pandas-matplotlib-bar-plots">1</a>, <a href="https://stackoverflow.com/questions/47741400/pandas-dataframe-group-and-sort-by-weekday?rq=1">2</a>, <a href="https://stackoverflow.com/questions/35193808/re-order-pandas-series-on-weekday">3</a>, to solve this but can't find method for using them in my case.</p>
  
  <p>Thank You all for hard work.</p>