大熊猫向后填补增量12个月

Question

我有一个包含每年课程名称的数据框.我需要找到从2016年开始的持续时间.

from io import StringIO

import pandas as pd

u_cols = ['page_id','web_id']
audit_trail = StringIO('''
year_id | web_id
2012|efg
2013|abc 
2014| xyz
2015| pqr
2016| mnp
''')

df11 = pd.read_csv(audit_trail, sep="|", names = u_cols  )

如何从最高位置开始在新列中添加月份(例如底部像bfill？)

最终的数据框架看起来像这样......

u_cols = ['page_id','web_id' , 'months']
audit_trail = StringIO('''
year_id | web_id | months
2012|efg | 60
2013|abc | 48
2014| xyz | 36
2015| pqr | 24
2016| mnp | 12
''')

df12 = pd.read_csv(audit_trail, sep="|", names = u_cols  )

---

有些答案并不认为可以有多门课程.更新样本数据......

from io import StringIO

import pandas as pd

u_cols = ['course_name','page_id','web_id']
audit_trail = StringIO('''
course_name| year_id | web_id
a|2012|efg
a|2013|abc 
a|2014| xyz
a|2015| pqr
a|2016| mnp
b|2014| xyz
b|2015| pqr
b|2016| mnp

''')

df11 = pd.read_csv(audit_trail, sep="|", names = u_cols  )

Answer 1

df11.assign(
    months=df11.groupby('course_name').apply(
        lambda x: pd.Series(np.repeat([12], len(x)).cumsum()[::-1])
    ).values
)

  course_name  year_id web_id  months
0           a     2012    efg      60
1           a     2013    abc      48
2           a     2014    xyz      36
3           a     2015    pqr      24
4           a     2016    mnp      12
5           b     2014    xyz      36
6           b     2015    pqr      24
7           b     2016    mnp      12

所有归功于@Alexander和@jezrael提醒我们一个很酷的特点transform
考虑到这一点,我可以改变我的回答

df11.assign(months=df11.groupby('course_name').year_id.transform(
    lambda x: np.repeat([12], len(x)).cumsum()[::-1]
))

  course_name  year_id web_id  months
0           a     2012    efg      60
1           a     2013    abc      48
2           a     2014    xyz      36
3           a     2015    pqr      24
4           a     2016    mnp      12
5           b     2014    xyz      36
6           b     2015    pqr      24
7           b     2016    mnp      12

Answer 2

>>> df11.assign(months=df11.groupby('course_name').year_id.transform(
        lambda years: range(len(years) * 12, 0, -12)))
  course_name  year_id web_id  months
0           a     2012    efg      60
1           a     2013   abc       48
2           a     2014    xyz      36
3           a     2015    pqr      24
4           a     2016    mnp      12
5           b     2014    xyz      36
6           b     2015    pqr      24
7           b     2016    mnp      12