问如何在一定条件下对数据进行计数

EN

res = (
    data.loc[data['CancellationCode'].eq('"B"'), 'FlightNum'].value_counts()
    .reindex(data.loc[data['CancellationCode'].notnull(), 'FlightNum']
                 .value_counts()[:5].index,
             fill_value=0)
)
print(res)
# 6    1
# 4    3
# 7    2
# 2    0
# 5    1
# Name: FlightNum, dtype: int64

table = df.dropna().assign(n=1).pivot_table(index='FlightNum',
                                            columns='CancellationCode',
                                            aggfunc='sum',
                                            margins=True,
                                            fill_value=0).droplevel(0,1)
>>> table
'''
CancellationCode  "A"  "B"  All
FlightNum                      
1                   0    1    1
2                   2    0    2
4                   0    3    3
5                   1    1    2
6                   3    1    4
7                   1    2    3
All                 7    8   15
'''
# the top 5 routes that were most often delayed
table.drop('All').nlargest(5,'All')

>>> out
'''
CancellationCode  "A"  "B"  All
FlightNum                      
6                   3    1    4
4                   0    3    3
7                   1    2    3
2                   2    0    2
5                   1    1    2
'''
# or to show only the number of delayed flights due to the weather ("B")
table.drop('All').nlargest(5,'All')['"B"']

>>> out
'''
FlightNum
6    1
4    3
7    2
2    0
5    1
Name: "B", dtype: int64