title: Can't find column names when using group by function in pandas dataframe
body: <p>I have a pandas dataframe, which looks like this: </p>
  
  <pre><code>   Country    City        POI       Type
  0   NL       Amsterdam    KFC       restaurant
  1   NL       Amsterdam    KFC       cafe
  2   NL       Arnhem     McDonalds   fast food
  3   NL       Arnhem     McDonalds   ice cream
  </code></pre>
  
  <p>I need to group by type column so I do not have duplicates in all other columns. In other words, I need an output like this: </p>
  
  <pre><code>   Country    City        POI       Type
  0   NL       Amsterdam    KFC       restaurant, cafe
  1   NL       Arnhem     McDonalds   fast food, ice cream
  </code></pre>
  
  <p>I tried to use group by function, but  all column names disappear, and shape function shows 0 columns. Maybe there is a better way to group those values? </p>
  
  <p>Here is a sample code:</p>
  
  <pre><code>import pandas as pd
  import numpy as np
  data = np.array([['','Country','City', 'POI', 'Type'],
              [0,"NL","Amsterdam", 'KFC', 'cafe'],
              [1,"NL","Amsterdam", 'KFC', 'restaurant'],
              [2,"NL","Arnhem", 'McDonalds', 'fast-food'],
              [3,"NL","Arnhem", 'McDonalds', 'ice cream']]
             )
  
  initial_df = pd.DataFrame(data=data[1:,1:],
                index=data[1:,0],
                columns=data[0,1:])
  
  final_df = initial_df .groupby( [ "Country", "City", "POI", "Type"] ).count()
  
  print(list(final_df.columns.values))
  print(final_df.shape)
  </code></pre>