How to subtract two DataFrame columns in Pandas

Question

I want to do some basic calculations inside a pandas dataframe, but apparently pandas ignores empty rows. So let's assume my dataframe looks as follows:

ColA ColB
11    6
7    

Then doing df["ColC"] = df["ColA"].subtract(df["ColB"]) will yield

ColA ColB ColC
11    6    5
7         

Whereas I would want that ColC also has a "7" in this case.

What's the best way to do these calculations with DataFrames?

Answer 1

我相信你需要参数fill_value=0 ：

df["ColC"] = df["ColA"].subtract(df["ColB"], fill_value=0)