在 pandas dataframe 中操作列表的有效方法

Question

I have a DataFrame that starts like the following:

	Column1	Column2
0	Berlin	['Hamburg', 'Munich', 'Berlin', 'Stuttgart']
1	Tokyo	['Tokyo', 'Osaka', 'Kyoto', 'Sapporo']
2	Los Angeles	['New York', 'Chicago', 'Boston', 'Los Angeles']
3	London	['Birmingham', 'London', 'Glasgow', 'Liverpool']

I would like to delete cities that exists in Column1 from Column2 lists such a way that DataFrame becomes like this:

	Column1	Column2
0	Berlin	['Hamburg', 'Munich', 'Stuttgart']
1	Tokyo	['Osaka', 'Kyoto', 'Sapporo']
2	Los Angeles	['New York', 'Chicago', 'Boston']
3	London	['Birmingham', 'Glasgow', 'Liverpool']

Since looping row by row is against the dataframe logic, what is the best way to approach this problem?

Answer 1

Try explode , query and gropuby :

(df.explode('Column2')
   .query('Column1 != Column2')
   .groupby(level=0)
   .agg({'Column1': 'first',
         'Column2': list
       })
)

Or just straight apply :

df['Column2'] = df.apply(lambda row: [x for x in row['Column2'] if x!=x['Column1']], 
                         axis=1)