复杂的 function 与 groupby 之间？ Python

Question

Here is a sample dataset.

import pandas as pd
import numpy as np
df = pd.DataFrame({ 
    'VipNo':np.repeat( range(3), 2 ),
    'Quantity': np.random.randint(200,size=6),
    'OrderDate': np.random.choice( pd.date_range('1/1/2020', periods=365, freq='D'), 6, replace=False)})
print(df)

So I have a couple of steps to do. I want to create a new column named qtywithin1mon/totalqty. First I want to group the VipNo (each number represents an individual) because a person may have made multiple purchases. Then I want to see if the orderdate is within a certain range (let's say 2020/03/01 - 2020/03/31). If so, I want to use the respective quantity on that day divided by the total quantity this customer purchased. My dataset is big so a customer may have ordered twice within the time range and I would want the sum of the two orders divided by the total quantity in this case. How can I achieve this goal? I really have no idea where to start..

Thank you so much!

Answer 1

You can create a new column masking quantity within the given date range, then groupby:

start, end = pd.to_datetime(['2020/03/01','2020/03/31'])

(df.assign(QuantitySub=df['OrderDate'].between(start,end)*df.Quantity)
   .groupby('VipNo')[['Quantity','QuantitySub']]
   .sum()
   .assign(output=lambda x: x['QuantitySub']/x['Quantity'])
   .drop('QuantitySub', axis=1)
)

With a data frame:

   VipNo  Quantity  OrderDate
0      0       105 2020-01-07
1      0        56 2020-03-04
2      1       167 2020-09-05
3      1        18 2020-05-08
4      2       151 2020-11-01
5      2        14 2020-03-17

The output is:

       Quantity    output
VipNo            
0           161  0.347826
1           185  0.000000
2           165  0.084848