How to compare Series string to another string in python

Question

I'm trying to compare a string from the Series to a string in Python. Here it seems to be ok - I get results of trues and falses:

domains_types['subtype'].astype(str) == 'Default'

for a file: print(domains_types)

But when I try to use it in "if", some problem appears: ValueError: The truth value of a Series is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all().

if domains_types['subtype'].astype(str) == 'Default':
    domains_types['Category'] = 'e-commerce'
else:
    domains_types['Category'] = 'other'

I'm new in Python, could you please explain there is the problem here and how to solve it?

I'd like to add a new column with a 'Category" according to the 'sybtype' result I want, here there is only "other" category so far

Answer 1

def cat(val):
    if val == 'Default':
        return('e-commerce')
    else:
        return('other')

df['Category'] = df.apply(lambda x: cat(x['Subtype']), axis=1)

This should return either 'other' or 'e-commerce' dependent on the value of each value in Subtype column. The issue with making an equivalence check against the whole series is explained above.

Or if you wanted to use a "normal" for loop you can iterate over the dataframe something like:

newcol = []

for index, row in df.iterrows():
    if row.Subtype == 'Default':
        newcol.append('e-commerce')
    else:
        newcol.append('other')

df['Category'] = newcol