Using groupby and cumsum to get a new column in pandas

Question

I have the following dataframe:

Class	Received	Issued
FD	10	0
FD	0	2
RM	5	0
RM	0	3
FD	0	2
PM	5	0
PM	1	0
RM	1	0
FD	4	0

I require the dataframe below:

Class	Received	Issued	Remaining Quantity
FD	10	0	10
FD	0	2	8
RM	5	0	5
RM	0	3	2
FD	0	2	6
PM	5	0	5
PM	1	0	6
RM	1	0	3
FD	4	0	10

The remaining quantity column is cumsum() of received - issued per class. I have tried different methods but I'm not getting it.

Answer 1

Another solution:

df["Remaining Quatity"] = (g := df.groupby("Class").cumsum())["Received"] - g["Issued"]
print(df)

Prints:

  Class  Received  Issued  Remaining Quatity
0    FD        10       0                 10
1    FD         0       2                  8
2    RM         5       0                  5
3    RM         0       3                  2
4    FD         0       2                  6
5    PM         5       0                  5
6    PM         1       0                  6
7    RM         1       0                  3
8    FD         4       0                 10

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OR: Using .pipe:

df["Remaining Quatity"] = df.groupby("Class").cumsum().pipe(lambda g: g["Received"] - g["Issued"])

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OR: Using .eval:

df["Remaining Quatity"] = df.groupby("Class").cumsum().eval("Received - Issued")