python - Pandas error when using if-else to create new column: The truth value of a Series is ambiguous

Question

I'm using Pandas and am trying to create a new column using a Python if-else statement (aka ternary condition operator) in order to avoid division by zero.

For example below, I want to create a new column C by dividing A/B. I want to use the if-else statement to avoid dividing by 0.

import pandas as pd
import numpy as np

df = pd.DataFrame(np.random.randint(0, 5, size=(100, 2)), columns=list('AB'))
df.head()
#    A  B
# 0  1  3
# 1  1  2
# 2  0  0
# 3  2  1
# 4  4  2

df['C'] = (df.A / df.B) if df.B > 0.0 else 0.0

However, I am getting an error from the last line:

ValueError: The truth value of a Series is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all().

I searched on StackOverflow and found other posts about this error, but none of them involved this type of if-else statement. Some posts include:

Truth value of a Series is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all()

The truth value of a Series is ambiguous in dataframe

Error: The truth value of a Series is ambiguous - Python pandas

Any help would be appreciated.

Answer 1

What about doing

>>> df['C'] = np.where(df.B>0., df.A/df.B, 0.)

which reads as :

where df.B is strictly positive, return df.A/df.B, otherwise return 0.