PANDAS Finding the exact word and before word in a column of string and append that new column in python (pandas) column

Question

Find the target word and the before word in col_a and append matched string in col_b_PY and col_c_LG columns

    This code i have tried to          


        

Answer 1

You may use

df['col_b_PY'] = df['col_a'].str.extract(r"([a-zA-Z'-]+\s+PY)\b")
df['col_c_LG'] = df['col_a'].str.extract(r"([a-zA-Z'-]+\s+LG)\b")

Or, to extract all matches and join them with a space:

df['col_b_PY'] = df['col_a'].str.extractall(r"([a-zA-Z'-]+\s+PY)\b").unstack().apply(lambda x:' '.join(x.dropna()), axis=1)
df['col_c_LG'] = df['col_a'].str.extractall(r"([a-zA-Z'-]+\s+LG)\b").unstack().apply(lambda x:' '.join(x.dropna()), axis=1)

Note you need to use a capturing group in the regex pattern so that extract could actually extract the text:

Extract capture groups in the regex pat as columns in a DataFrame.

Note the \b word boundary is necessary to match PY / LG as a whole word.

Also, if you want to only start a match from a letter, you may revamp the pattern to

r"([a-zA-Z][a-zA-Z'-]*\s+PY)\b"
r"([a-zA-Z][a-zA-Z'-]*\s+LG)\b"
   ^^^^^^^^          ^

where [a-zA-Z] will match a letter and [a-zA-Z'-]* will match 0 or more letters, apostrophes or hyphens.

Python 3.7 with Pandas 0.24.2:

pd.set_option('display.width', 1000)
pd.set_option('display.max_columns', 500)

df = pd.DataFrame({
    'col_a': ['Python PY is a general-purpose language LG',
             'Programming language LG in Python PY',
             'Its easier LG to understand  PY',
             'The syntax of the language LG is clean PY',
             'Python PY is a general purpose PY language LG']
    })
df['col_b_PY'] = df['col_a'].str.extractall(r"([a-zA-Z'-]+\s+PY)\b").unstack().apply(lambda x:' '.join(x.dropna()), axis=1)
df['col_c_LG'] = df['col_a'].str.extractall(r"([a-zA-Z'-]+\s+LG)\b").unstack().apply(lambda x:' '.join(x.dropna()), axis=1)

Output:

                                           col_a              col_b_PY     col_c_LG
0     Python PY is a general-purpose language LG             Python PY  language LG
1           Programming language LG in Python PY             Python PY  language LG
2                Its easier LG to understand  PY        understand  PY    easier LG
3      The syntax of the language LG is clean PY              clean PY  language LG
4  Python PY is a general purpose PY language LG  Python PY purpose PY  language LG

Answer 2

Check with

df['col_c_LG'],df['col_c_PY']=df['col_a'].str.extract(r"(\w+\s+LG)"),df['col_a'].str.extract(r"(\w+\s+PY)")
df
Out[474]: 
                                        col_a       ...              col_c_PY
0  Python PY is a general-purpose language LG       ...             Python PY
1       Programming language LG in Python PY        ...             Python PY
2             Its easier LG to understand  PY       ...        understand  PY
3   The syntax of the language LG is clean PY       ...              clean PY
[4 rows x 3 columns]