Python Pandas-检查子字符串是否包含并将新列设置为子字符串

Question

I need to check for string containment and set the new column to the substring value. I am currently trying this

df['NEW_COL'] = df['COL_TO_CHECK'].str.contains('|'.join(substring_list))

instead of returning the boolean true false for containment... I need to return the actual value from substring_list that matches to populate df['NEW_COL]

SUBSTRINGS TO CHECK FOR

substring_list = ['apple', 'banana', 'cherry']

RESULTING DATAFRAME

OLD_COL              NEW_COL
apple pie            apple
black cherry         cherry
banana lemon drop    banana

Answer 1

You are not being very insightful regarding what is your data and what you want, but the general principle is that you can use:

df['NEW_COL'] = df['COL_TO_CHECK'].apply(lambda x: do_something(x) if is_something(x) else x)

Or in your example:

substring_list = set(['apple', 'banana', 'cherry'])
df['NEW_COL'] = df['OLD_COL'].apply(lambda x: set(x.split()).intersection(substring_list).pop())

set is faster :)

Answer 2

I'd do it this way:

In [148]: df
Out[148]:
             OLD_COL
0          apple pie
1       black cherry
2  banana lemon drop

In [149]: pat = '.*({}).*'.format('|'.join(substring_list))

In [150]: pat
Out[150]: '.*(apple|banana|cherry).*'

In [151]: df['NEW_COL'] = df['OLD_COL'].str.replace(pat, r'\1')

In [152]: df
Out[152]:
             OLD_COL NEW_COL
0          apple pie   apple
1       black cherry  cherry
2  banana lemon drop  banana