Extract strings from columns using regex

Question

I want to extract the following strings from the title column and append to a new column named hazard_extract like in the below example.

test = {'title': ['Other', 'Microbiological - Listeria', 'Extraneous Material', 'Chemical', 'Chemical - Histamine', 'Labelling, Other'], 'hazard_extract':['Other', 'Microbiological', 'Extraneous Material', 'Chemical', 'Chemical', 'Labelling']}
example = pd.DataFrame(test)
example


    title                       hazard_extract
0   Other                       Other
1   Microbiological - Listeria  Microbiological
2   Extraneous Material         Extraneous Material
3   Chemical                    Chemical
4   Chemical - Histamine        Chemical
5   Labelling, Other            Labelling

However, I am using the code below - if the string does not have a - or , it does not extract the string. In this case, how can I extract both words as in Extraneous Material and a single word as in Chemical or Other?

example['hazard_extract'] = example['title'].str.extract(r'^(.*?),? ')

    title                       hazard_extract
0   Other                       NaN
1   Microbiological - Listeria  Microbiological
2   Extraneous Material         Extraneous
3   Chemical                    NaN
4   Chemical - Histamine        Chemical
5   Labelling, Other            Labelling

Thank you so much for all the help!

so if there is a dash/comma, you want the part before the dash/comma; otherwise you want the full original string? — tdy
– tdy, Commented Mar 15, 2021 at 4:30

Epsi95 · Accepted Answer · 2021-03-15 04:41:03Z

1

The easiest will be to use split

example['title'].str.split(r'[-,]').str[0].str.strip()

0                  Other
1       Microbiological 
2    Extraneous Material
3               Chemical
4              Chemical 
5              Labelling

edited Mar 15, 2021 at 4:41

answered Mar 15, 2021 at 4:35

Epsi95

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2 Comments

tdy Over a year ago

maybe add .str.strip()?

Epsi95 Over a year ago

I was thinking about that but since OP needs the first element and - , comes right after the first word, though not required

Mark Tolonen · Accepted Answer · 2021-03-15 04:41:34Z

No need for a complicated regular expression:

import pandas as pd

test = {'title': ['Other', 'Microbiological - Listeria', 'Extraneous Material', 'Chemical', 'Chemical - Histamine', 'Labelling, Other']}
example = pd.DataFrame(test)
print(example)
print()
example['hazard_extract'] = example['title'].str.split(' -|,').str[0]
print(example)

                        title
0                       Other
1  Microbiological - Listeria
2         Extraneous Material
3                    Chemical
4        Chemical - Histamine
5            Labelling, Other

                        title       hazard_extract
0                       Other                Other
1  Microbiological - Listeria      Microbiological
2         Extraneous Material  Extraneous Material
3                    Chemical             Chemical
4        Chemical - Histamine             Chemical
5            Labelling, Other            Labelling

ashkangh · Accepted Answer · 2021-03-15 04:34:55Z

0

Try this:

example['title'].str.extract(r'^(\w*\s*\w*)\s*[\,\-]?.*')

edited Mar 15, 2021 at 4:34

answered Mar 15, 2021 at 4:32

ashkangh

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