python - Check if a string in a Pandas DataFrame column is in a list of strings

Question

If I have a frame like this

frame = pd.DataFrame({'a' : ['the cat is blue', 'the sky is green', 'the dog is black']})

and I want to check if any of those rows contain a certain word I just have to do this.

frame['b'] = frame.a.str.contains("dog") | frame.a.str.contains("cat") | frame.a.str.contains("fish")

frame['b'] outputs:

True
False
True

If I decide to make a list

mylist =['dog', 'cat', 'fish']

how would I check that the rows contain a certain word in the list?

Answer 1

frame = pd.DataFrame({'a' : ['the cat is blue', 'the sky is green', 'the dog is black']})

frame
                  a
0   the cat is blue
1  the sky is green
2  the dog is black

The str.contains method accepts a regular expression pattern:

mylist = ['dog', 'cat', 'fish']
pattern = '|'.join(mylist)

pattern
'dog|cat|fish'

frame.a.str.contains(pattern)
0     True
1    False
2     True
Name: a, dtype: bool

Because regex patterns are supported, you can also embed flags:

frame = pd.DataFrame({'a' : ['Cat Mr. Nibbles is blue', 'the sky is green', 'the dog is black']})

frame
                     a
0  Cat Mr. Nibbles is blue
1         the sky is green
2         the dog is black

pattern = '|'.join([f'(?i){animal}' for animal in mylist])  # python 3.6+

pattern
'(?i)dog|(?i)cat|(?i)fish'
 
frame.a.str.contains(pattern)
0     True  # Because of the (?i) flag, 'Cat' is also matched to 'cat'
1    False
2     True

Answer 2

For list should work

print frame[frame['a'].isin(mylist)]     

http://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.isin.html

Answer 3

After going through the comments of the accepted answer of extracting the string, this approach can also be tried.

frame = pd.DataFrame({'a' : ['the cat is blue', 'the sky is green', 'the dog is black']})

frame
              a
0   the cat is blue
1  the sky is green
2  the dog is black

Let us create our list which will have strings that needs to be matched and extracted.

mylist = ['dog', 'cat', 'fish']
pattern = '|'.join(mylist)

Now let create a function which will be responsible to find and extract the substring.

import re
def pattern_searcher(search_str:str, search_list:str):

    search_obj = re.search(search_list, search_str)
    if search_obj :
        return_str = search_str[search_obj.start(): search_obj.end()]
    else:
        return_str = 'NA'
    return return_str

We will use this function with pandas.DataFrame.apply

frame['matched_str'] = frame['a'].apply(lambda x: pattern_searcher(search_str=x, search_list=pattern))

Result :

              a             matched_str
   0   the cat is blue         cat
   1  the sky is green         NA
   2  the dog is black         dog

Answer 4

We can check for three patterns simultaneously using pipe, for example

for i in range(len(df)):
       if re.findall(r'car|oxide|gen', df.iat[i,1]):
           df.iat[i,2]='Yes'
       else:
           df.iat[i,2]='No'