正则表达式仅匹配子目标题

Question

我有一个带有标题的列的数据框（见下面的示例）

import numpy as np




Fairytales_in = {'Titles': ['Fairy Tales',
                    'Tales.3.2.Dancing Shoes, ballgowns and frogs',
                    'Tales.2.4.6.Red Riding Hood',
                    'Fairies.1Your own Fairy godmother',
                    'Ogres-1.1.The wondrous world of Shrek',
                    'Witches-1-4Maleficient and the malicious curse',
                    'Tales.2.1.The big bad wolf',
                    'Tales.2.Little Red riding Hood',
                    'Tales.2.4.6.1.Why the huntsman is underrated',
                    'Tales.5.f.Cinderella and the pumpkin carriage',
                    'Ogres-1.Best Ogre in town',
                    'No.3.Great Expectations']}

    Fairytales_in = pd.DataFrame.from_dict(Fairytales_in)

我想创建一个新列，它包含与标题列完全相同的字符串，但只有当它是副标题时。（例如，故事集3.2.或食人魔-1.1.或女巫-1-4或故事集5.f）

This would be my expected output: 


    Fairytales_expected_output = {'Titles': ['Fairy Tales',
                    'Tales.3.2.Dancing Shoes, ballgowns and frogs',
                    'Tales.2.4.6.Red Riding Hood',
                    'Fairies.1Your own Fairy godmother',
                    'Ogres-1.1.The wondrous world of Shrek',
                    'Witches-1-4Maleficient and the malicious curse',
                    'Tales.2.1.The big bad wolf',
                    'Tales.2.Little Red riding Hood',
                    'Tales.2.4.6.1.Why the huntsman is underrated',
                    'Tales.5.f.Cinderella and the pumpkin carriage',
                    'Ogres-1.Best Ogre in town',
                    'No.3.Great Expectations'],
                    'Subheading': ['NaN', 
                                   'Tales.3.2.Dancing Shoes, ballgowns and frogs',
                                   'NaN',
                                   'NaN',
                                   'Ogres-1.1.The wondrous world of Shrek',
                                   'Witches-1-4Maleficient and the malicious curse',
                                   'Tales.2.1.The big bad wolf',
                                   'NaN',
                                   'NaN',
                                   'Tales.5.f.Cinderella and the pumpkin carriage',
                                   'NaN',
                                   'NaN']}

    Fairytales_expected_output = pd.DataFrame.from_dict(Fairytales_expected_output)

我一直在努力寻找一种方法，使我的模式只匹配副标题。无论我尝试什么，第一级或第三级标题仍然包括在内This question的要求或多或少是一样的，但它是用C#编写的，我无法使它在我的用例中工作

这就是我迄今为止所尝试的：

Fairytales_in['Subheading'] = Fairytales_in.Titles.str.extract(r'(^(?:\w+\.|\-\d{1}\.\d{1}\.)\W*(?:\w+\b\W*){1,100})$')

但正如你所看到的，它并没有产生预期的结果。我一直在尝试使用regex101.com，但我已经在这上面坚持了两天了。如果您能帮我修改图案，我们将不胜感激

Answer 1

你可以用

rx = r'^(\w+(?:[.-](?:\d+|[a-zA-Z]\b)){2}(?![.-]?\d).*)'
Fairytales_in['Subheading'] = Fairytales_in['Titles'].str.extract(rx, expand=False)

见regex demo

详细信息

• ^-字符串的开头
• \w+-1个或多个单词字符
• (?:[.-](?:\d+|[a-zA-Z]\b)){2}-两次出现
  • [.-]-一个点或-
  • (?:\d+|[a-zA-Z]\b)-1个或多个数字或后跟单词边界的ASCII字母
• (?![.-]?\d)-没有可选的.或-后跟当前位置右侧允许的数字
• .*-除换行符以外的任何0个或更多字符，尽可能多

熊猫测试：

>>> Fairytales_in['Titles'].str.extract(rx, expand=False)
0                                                NaN
1       Tales.3.2.Dancing Shoes, ballgowns and frogs
2                                                NaN
3                                                NaN
4              Ogres-1.1.The wondrous world of Shrek
5     Witches-1-4Maleficient and the malicious curse
6                         Tales.2.1.The big bad wolf
7                                                NaN
8                                                NaN
9      Tales.5.f.Cinderella and the pumpkin carriage
10                                               NaN
11                                               NaN
Name: Titles, dtype: object