python - 按列降序排序

Question

sample = pd.DataFrame({'Cat':['A','B','C','A','B','C','A','B','C'], 
                       'Year':[2001,2002,2003,2001,2002,2003,2001,2002,2003]})

for s in sample.groupby(['Year']):
    print s[0]

这会给

2001
2002
2003

如何按降序对 groupby 结果进行排序以获得 ..

2003
2002
2001

Answer 1

我认为最好的办法是提前对帧进行降序排序，并将 sort=False 传递给 groupby 操作，这样数据就不会重新排序。

In [78]: sample = sample.sort(['Year'], ascending=False)

In [79]: for s in sample.groupby(['Year'], sort=False):
    ...:     print s[0]
    ...:     
2003
2002
2001