If-statement with pandas throws “ValueError: The truth value of a Series is ambiguous”

Question

I am wanting to see if a particular string is present in my dataframe for one column and fire off an API if it is. code so far:

if new_df.col1.str.contains(\'str         


        

Answer 1

The reason for this error is because if-else expressions in python are meant to compare scalar boolean values. You passed a Series.

See more in docs section on Pandas Gotchas.

pandas follows the NumPy convention of raising an error when you try to convert something to a bool. This happens in an if-statement or when using the boolean operations: and, or, and not.

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In this example, you can combine them into a single regex pattern 'string2?' which indicates that '2' is optional.

def make_request():
    ...

for mask in new_df.col1.str.contains(r'string2?'):
    if mask:
        make_request()

If your make_request function returns something, you can call it in a list comp and assign back:

df['response'] = [
    make_request() if m else np.nan for m in new_df.col1.str.contains(r'string2?')]

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Another option is using regex OR pipe to join strings in a list.

import re

words = ['string', 'string2']
for mask in new_df.col1.str.contains('|'.join(map(re.escape, words))):
    ...