一个简短的 Dataframe ，我想：
1.按分钟排列
1.添加缺失分钟的行，从09：05到09：20
1.然后每5分钟重新取样一次

time  cars     flow
 0  9:07   737       In
 1  9:06    22      Out
 2  9:18    42       In
 3  9:19    36  Unknown

我尝试的是：

data = {'time': ["9:07", "9:06", "9:18", "9:19"], 
'cars' : [737,  22, 42,36],
'flow': ["In","Out","In","Unknown"]}

df = pd.DataFrame(data)
idx = pd.date_range("9:05", "09:20", freq="1min")
idx = idx.rename('time')

df = df.set_index('time')
df.index = pd.to_datetime(df.index)
df = df.reindex(idx, fill_value=0)

df = df.groupby('flow').resample('5T')['cars'].sum()     # how_many_volume
print(df)

它返回：

flow     time               
0        2020-10-21 09:05:00      0
         2020-10-21 09:10:00      0
         2020-10-21 09:15:00      0
         2020-10-21 09:20:00      0
In       2020-10-21 09:05:00    737
         2020-10-21 09:10:00      0
         2020-10-21 09:15:00     42
Out      2020-10-21 09:05:00     22
Unknown  2020-10-21 09:15:00     36

但我们想要的是

In             2020-10-21 09:05:00    737
               2020-10-21 09:10:00    0
               2020-10-21 09:15:00    42
               2020-10-21 09:20:00    0
Out            2020-10-21 09:05:00    22
               2020-10-21 09:10:00    0
               2020-10-21 09:15:00    0
               2020-10-21 09:20:00    0
Unknown        2020-10-21 09:05:00    0
               2020-10-21 09:10:00    0
               2020-10-21 09:15:00    36
               2020-10-21 09:20:00    0

实现它的方法是什么？