删除第二个插入符正则表达式后的所有内容并应用于 pandas dataframe 列

Question

I have a dataframe with a column that looks like this:

0         EIAB^EIAB^6
1           8W^W844^A
2           8W^W844^A
3           8W^W858^A
4           8W^W844^A
             ...     
826136    EIAB^EIAB^6
826137    SICU^6124^A
826138    SICU^6124^A
826139    SICU^6128^A
826140    SICU^6128^A

I just want to keep everything before the second caret, eg: 8W^W844 , what regex would I use in Python? Similarly PACU^SPAC^06 would be PACU^SPAC . And to apply it to the whole column.

I tried r'[\\^].+$' since I thought it would take the last caret and everything after, but it didn't work.

Answer 1

You can negate the character group to find everything except ^ and put it in a match group. you don't need to escape the ^ in the character group but you do need to escape the one outside.

re.match(r"([^^]+\^[^^]+)", "8W^W844^A").group(1)

This is quite useful in a pandas dataframe. Assuming you want to do this on a single column you can extract the string you want with

df['col'].str.extract(r'^([^^]+\^[^^]+)', expand=False)

NOTE

Originally, I used replace , but the extract solution suggested in the comments executed in 1/4 the time.

import pandas as pd
import numpy as np
from timeit import timeit

df = pd.DataFrame({"foo":np.arange(1_000_000)})
df["bar"] = "8W^W844^A"
df2 = df.copy()

def t1():
    df.bar.str.replace(r"([^^]+\^[^^]+).*", r"\1", regex=True)
    
def t2():
    df.bar.str.extract(r'^([^^]+\^[^^]+)', expand=False)

print("replace", timeit("t1()", globals=globals(), number=20))
print("extract", timeit("t2()", globals=globals(), number=20))
                                                     

output

replace 39.73989862400049
extract 9.910304663004354

Answer 2

I don't think regex is really necessary here, just slice the string up to the position of the second caret:

>>> s = 'PACU^SPAC^06'
>>> s[:s.find("^", s.find("^") + 1)]
'PACU^SPAC'

Explanation : str.find accepts a second argument of where to start the search, place it just after the position of the first caret.