Insert word at beginning of row – python

December 12, 2023

I want to insert a word at the beginning of a string for each row in a column where the first word is not x. If it is x, then move on. For below, x = BP. So if first word in cat is not BP, then insert it.

df = pd.DataFrame({ 
   'cat': ['BP STATION', 'STATION', 'BP OLD', 'OLD OLD'],    
   })

df['cat'] = df['cat'].str.replace(r'^\w+', 'BP')

intent:

             cat
0     BP STATION
1     BP STATION
2         BP OLD
3     BP OLD OLD

>Solution :

You need your search regex to be "not BP" and you need to capture it so that it doesn’t get removed in the replacement. So you wantr'^([^B][^P]). And the replacement regex is then r'BP \1'.

>>> df['cat'] = df['cat'].str.replace(r'^([^B][^P])', r'BP \1')
<stdin>:1: FutureWarning: The default value of regex will change from True to False in a future version.
>>> df
          cat
0  BP STATION
1  BP STATION
2      BP OLD
3  BP OLD OLD
>>>