Conditional computing on pandas dataframe with an if statement

Question

I have the following df:

A     B    C
100   2    3
-100  2    3

I want a new column that multiplies either column B or C by the value of column A:

if A<0:
D = A*B

if A>=0:
D = A*C

So in the end I get:

A     B    C   D
100   2    3   200
-100  2    3   -300

Answer 1

You could run a lambda function based on what you are looking like this:

df["D"] = df.apply(lambda row: row["A"] * row["B"] if row["A"] < 0 else row["A"] * row["C"], axis=1)