python - Pandas |分组数据框中的 Fillna(ffill) 未填充

Question

我有一个 MultIndex 数据帧，并尝试填充一个值 MAX_PTS_YR，以便 t+1 年的 MAX_PTS_YR 值 > 等于 t 中的 MAX_PTS_YR。

因此:2016 中的 MAX_PTS_YR 应等于 116。

使用 nth，我找到了前一年的 MAX_PTS:

DF['MAX_PTS_YR'] = DF.groupby(by=['Affiliation','Year'],as_index=False)['PtsYr'].nth(-1)


Affiliation mkid        Year    PtsYr  MAX_PTS_YR
MVPAFL0003  10176228    2015    96.0    NaN
MVPAFL0003  10176228    2015    96.0    NaN
MVPAFL0003  10176228    2015    106.0   NaN
MVPAFL0003  10176228    2015    116.0   116.0
MVPAFL0003  10176228    2016    10.0    NaN
MVPAFL0003  10176228    2016    10.0    NaN
MVPAFL0003  10176228    2016    20.0    NaN
MVPAFL0003  10176228    2016    20.0    NaN
MVPAFL0003  10176228    2016    30.0    NaN
MVPAFL0003  10176228    2016    40.0    NaN
MVPAFL0003  10176228    2016    50.0    NaN
MVPAFL0003  10176228    2016    50.0    NaN
MVPAFL0003  10176228    2016    52.0    NaN
MVPAFL0003  10176228    2016    62.0    NaN
MVPAFL0003  10176228    2016    62.0    NaN
MVPAFL0003  10176228    2016    82.0    NaN
MVPAFL0003  10176228    2016    94.0    NaN
MVPAFL0003  10176228    2016    94.0    NaN
MVPAFL0003  10176228    2016    94.0    NaN
MVPAFL0003  10176228    2016    104.0   NaN
MVPAFL0003  10176228    2016    114.0   114.0

我想我可以fillna加入那个隶属组:

DF.groupby(by=['Affiliation'],as_index=False)['MAX_PTS_AFFIL'].fillna(method='ffill',inplace=True)

但是当我这样做时，没有填充 NaN 值。

有什么想法吗？

Answer 1

# get just the series you are filling to simplify things
s1 = df.set_index(['Affiliation', 'Year']).MAX_PTS_YR

# groupby to get the max per group
mx = s1.groupby(level=[0, 1]).max()

# shift your year index by one year
mx.index.set_levels(mx.index.levels[1] + 1, 1, inplace=True)

# fill in missing bits
s1.fillna(mx)

<小时/>

Affiliation  Year
MVPAFL0003   2015      NaN
             2015      NaN
             2015      NaN
             2015    116.0
             2016    116.0
             2016    116.0
             2016    116.0
             2016    116.0
             2016    116.0
             2016    116.0
             2016    116.0
             2016    116.0
             2016    116.0
             2016    116.0
             2016    116.0
             2016    116.0
             2016    116.0
             2016    116.0
             2016    116.0
             2016    116.0
             2016    114.0
Name: MAX_PTS_YR, dtype: float64

<小时/>

现在分配给 df

df.MAX_PTS_YR = (s1.fillna(mx).values)
df