Python Pandas：两个数据帧之间数据的条件减法？

Question

I'm trying to use conditional subtraction between two dataframes.

Dataframe df1 has columns name and price.name is not unique.

>>df1
        name   price
    0  mark     50
    1  mark     200
    2  john     10
    3  chris    500

Another dataframe has two columns name and paid , Here name is unique

>>df2
       name      paid
    0  mark     150
    1  john     10

How can I conditionally subtract both dataframes to get following output

Final Output expected

       name     price  paid
    0  mark     50     50
    1  mark     200    100
    2  john     10     10
    3  chris    500     0

Answer 1

IIUC, you can use:

# mapper for paid values
s = df2.set_index('name')['paid']

df1['paid'] = (df1
      .groupby('name')['price']  # for each name
      .apply(lambda g: g.cumsum()  # sum the total owed
                        .clip(upper=s.get(g.name, default=0)) # in the limit of the paid
                        .pipe(lambda s: s.diff().fillna(s))   # compute reverse cumsum
            )
     )

output:

    name  price   paid
0   mark     50   50.0
1   mark    200  100.0
2   john     10   10.0
3  chris    500    0.0