Python Pandas - group by keys 与重复值的区别

Question

我有一些关于向客户销售日期的数据。数据如下所示：

	Cod client	Items	Date
0	100	1	2022/01/01
1	100	7	2022/01/01
2	100	2	2022/02/01
3	101	5	2022/01/01
4	101	8	2022/02/01
5	101	10	2022/02/01
6	101	2	2022/04/01
7	101	2	2022/04/01
8	102	4	2022/02/01
9	102	10	2022/03/01

我要完成的是计算每个客户日期之间的差异：首先按“Cod client”分组，然后按“Date”分组（因为重复）

预期结果如下：

	Cod client	Items	Date	Date diff	Explain
0	100	1	2022/01/01	NaT	First date for client 100
1	100	7	2022/01/01	NaT	...repeat above
2	100	2	2022/02/01	31	Diff from first date 2022/01/01
3	101	5	2022/01/01	NaT	Fist date for client 101
4	101	8	2022/02/01	31	Diff from first date 2022/01/01
5	101	10	2022/02/01	31	...repeat above
6	101	2	2022/04/01	59	Diff from previous date 2022/02/01
7	101	2	2022/04/01	59	...repeat above
8	102	4	2022/02/01	NaT	First date for client 102
9	102	10	2022/03/01	28	Diff from first date 2022/02/01

我已经尝试过 df["Date diff"] = df.groupby("Cod client")["Date"].diff() 但它考虑了重复日期和 return 零

感谢您的帮助！

Answer 1

IIUC 您可以组合多个 groupby 操作：

# ensure datetime
df['Date'] = pd.to_datetime(df['Date'])

# set up group
g = df.groupby('Cod client')

# identify duplicated dates per group
m = g['Date'].apply(pd.Series.duplicated)

# compute the diff, mask and ffill
df['Date diff'] = g['Date'].diff().mask(m).groupby(df['Cod client']).ffill()

输出：

   Cod client  Items       Date Date diff
0         100      1 2022-01-01       NaT
1         100      7 2022-01-01       NaT
2         100      2 2022-02-01   31 days
3         101      5 2022-01-01       NaT
4         101      8 2022-02-01   31 days
5         101     10 2022-02-01   31 days
6         101      2 2022-04-01   59 days
7         101      2 2022-04-01   59 days
8         102      4 2022-02-01       NaT
9         102     10 2022-03-01   28 days

Answer 2

另一种方法，transform:

import pandas as pd
# data saved as .csv
df = pd.read_csv("Data.csv", header=0, parse_dates=True)
# convert Date column to correct date.
df["Date"] = pd.to_datetime(df["Date"], format="%d/%m/%Y")
# new column!
df["Date diff"] = df.sort_values("Date").groupby("Cod client")["Date"].transform(lambda x: x.diff().replace("0 days", pd.NaT).ffill())

Python Pandas - group by keys 与重复值的区别

Python Pandas - Difference between groupby keys with repeated valyes

python

pandas

dataframe

numpy

pandas-groupby