How to separate strings from a column in pandas?

Question

I have 2 columns:

A	B
1	ABCSD
2	SSNFs
3 CVY KIP
4 MSSSQ
5	ABCSD
6 MMS LLS
7	QQLL

This is an example actual files contains these type of cases in 1000+ rows.
I want to separate all the alphabets from column A and get them as output in column B:
Expected Output:

A	B
1	ABCSD
2	SSNFs
3	CVY KIP
4	MSSSQ
5	ABCSD
6	MMS LLS
7	QQLL

So Far I have tried this which works but looking for a better way:


df['B2'] = df['A'].str.split(' ').str[1:]

def try_join(l):
    try:
        return ' '.join(map(str, l))
    except TypeError:
        return np.nan
df['B2'] = [try_join(l) for l in df['B2']]

df = df.replace('', np.nan)
append=df['B2']
df['B']=df['B'].combine_first(append)
df['A']=[str(x).split(' ')[0] for x in df['A']]
df.drop(['B2'],axis=1,inplace=True)
df

Asked By: redox741

||

Source

Answer 1

You could try as follows.

Either use str.extractall with two named capture groups (generic: (?P<name>...)) as A and B. First one for the digit(s) at the start, second one for the rest of the string. (You can easily adjust these patterns if your actual strings are less straightforward.) Finally, drop the added index level (1) by using df.droplevel.
Or use str.split with n=1 and expand=True and rename the columns (0 and 1 to A and B).
Either option can be placed inside df.update with overwrite=True to get the desired outcome.

import pandas as pd
import numpy as np

data = {'A': {0: '1', 1: '2', 2: '3 CVY KIP', 3: '4 MSSSQ', 
              4: '5', 5: '6 MMS LLS', 6: '7'}, 
        'B': {0: 'ABCSD', 1: 'SSNFs', 2: np.nan, 3: np.nan, 
              4: 'ABCSD', 5: np.nan, 6: 'QQLL'}
        }

df = pd.DataFrame(data)

df.update(df.A.str.extractall(r'(?P<A>^d+)s(?P<B>.*)').droplevel(1), 
          overwrite=True)

# or in this case probably easier:
# df.update(df.A.str.split(pat=' ', n=1, expand=True)
#          .rename(columns={0:'A',1:'B'}),overwrite=True)

df['A'] = df.A.astype(int)

print(df)

   A        B
0  1    ABCSD
1  2    SSNFs
2  3  CVY KIP
3  4    MSSSQ
4  5    ABCSD
5  6  MMS LLS
6  7     QQLL

Answered By: ouroboros1

Answer 2

You could use str.split() if your number appears first.

df['A'].str.split(n=1,expand=True).set_axis(df.columns,axis=1).combine_first(df)

or

df['A'].str.extract(r'(?P<A>d+) (?P<B>[A-Za-z ]+)').combine_first(df)

Output:

   A        B
0  1    ABCSD
1  2    SSNFs
2  3  CVY KIP
3  4    MSSSQ
4  5    ABCSD
5  6  MMS LLS
6  7     QQLL

Answered By: rhug123

Answer 3

You can split on ' ' as it seems that the numeric value is always at the beginning and the text is after a space.

split = df.A.str.split(' ', 1)
df.loc[df.B.isnull(), 'B'] = split.str[1]
df.loc[:, 'A'] = split.str[0]

Answered By: T C Molenaar

How to separate strings from a column in pandas?

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