python - 如何根据多个条件用字符串拆分 Pandas 数据框列

Question

我有一个 Pandas 数据框，如下所示:

    ID       Col.A

28654      This is a dark chocolate which is sweet 
39876      Sky is blue 1234 Sky is cloudy 3423
88776      Stars can be seen in the dark sky
35491      Schools are closed 4568 but shops are open

我试图在单词 Col.A 或 dark 之前拆分 digits 。我想要的结果如下。

     ID             Col.A                             Col.B
    
    28654      This is a                  dark chocolate which is sweet 
    39876      Sky is blue                1234 Sky is cloudy 3423
    88776      Stars can be seen in the   dark sky
    35491      Schools are closed         4568 but shops are open

我尝试将包含单词 dark 的行分组到一个数据帧，并将带有数字的行分组到另一个数据帧，然后相应地拆分它们。之后，我可以连接生成的数据帧以获得预期的结果。代码如下:

df = pd.DataFrame({'ID':[28654,39876,88776,35491], 'Col.A':['This is a dark chocolate which is sweet', 
                                                            'Sky is blue 1234 Sky is cloudy 3423', 
                                                            'Stars can be seen in the dark sky',
                                                            'Schools are closed 4568 but shops are open']})

df1 = df[df['Col.A'].str.contains(' dark ')==True]
df2 = df.merge(df1,indicator = True, how='left').loc[lambda x : x['_merge']!='both']
df1 = df1["Col.A"].str.split(' dark ', expand = True)
df2 = df2["Col.A"].str.split('\d+', expand = True)
pd.concat([[df1, df2], axis =0)

得到的结果与预期的不同。那是，

      0                              1
0   This is a                   chocolate which is sweet
2   Stars can be seen in the     sky    
1   Sky is blue                  Sky is cloudy  
3   Schools are closed           but shops are open

我错过了字符串中的数字和结果中的单词 dark。
那么如何解决这个问题并获得结果而不遗漏拆分单词和数字呢？
有没有办法在不删除它们的情况下“在预期的单词或数字之前切片”？

Answer 1

Series.str.split

s = df['Col.A'].str.split(r'\s+(?=\b(?:dark|\d+)\b)', n=1, expand=True)
df[['ID']].join(s.set_axis(['Col.A', 'Col.B'], 1))

      ID                     Col.A                          Col.B
0  28654                 This is a  dark chocolate which is sweet
1  39876               Sky is blue        1234 Sky is cloudy 3423
2  88776  Stars can be seen in the                       dark sky
3  35491        Schools are closed        4568 but shops are open

正则表达式详细信息:

\s+ : 匹配任意空白字符一次或多次

(?=\b(?:dark|\d+)\b) : 正向预测

\b : 防止部分匹配的词边界

(?:dark|\d+) : 非捕获组

dark : First Alternative 匹配字符暗字

\d+ : 匹配任何数字一次或多次的第二种选择

\b : 防止部分匹配的词边界

查看在线 regex demo