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python - 如何根据多个条件用字符串拆分 Pandas 数据框列

问题描述

我有一个熊猫数据框，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Col.A在 worddark或digits. 我想要的结果如下所示。

     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

我试图将包含单词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dark结果中的单词。

那么如何解决这个问题并在不丢失拆分单词和数字的情况下获得结果呢？

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”？

标签： pythonregexpandasdataframe

解决方案

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+: 匹配任何空白字符一次或多次
  • (?=\b(?:dark|\d+)\b): 积极的前瞻
    • \b：字边界以防止部分匹配
    • (?:dark|\d+): 非捕获组
      • dark: First Alternative 从字面上匹配暗字符
      • \d+：第二种选择，匹配任何数字一次或多次
    • \b：字边界以防止部分匹配

见网上regex demo

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