在同一列中提取多个字符串组

Question

我有以下数据帧：

test = {'title': ['Undeclared milk in Burnbrae', 'Undeclared milk in certain Bumble', 'Certain cheese products may contain listeria', 'Ocean brand recalled due to Salmonella', 'IQF Raspberries due to Listeria']}
example = pd.DataFrame(test)
example

    title
0   Undeclared milk in Burnbrae
1   Undeclared milk in certain Bumble
2   Certain cheese products may contain listeria
3   Ocean brand recalled due to Salmonella
4   IQF Raspberries due to Listeria

我想在同一列中提取以下字符串。我希望我的结果如下所示：

test = {'hazard': ['Undeclared milk', 'Undeclared milk', 'listeria', 'Salmonella', 'Listeria'], 'title': ['Undeclared milk in Burnbrae', 'Undeclared milk in certain Bumble', 'Certain cheese products may contain listeria', 'Ocean brand recalled due to Salmonella', 'IQF Raspberries due to Listeria']}
example2 = pd.DataFrame(test)
example2

     hazard          title
0   Undeclared milk Undeclared milk in Burnbrae
1   Undeclared milk Undeclared milk in certain Bumble
2   listeria        Certain cheese products may contain listeria
3   Salmonella      Ocean brand recalled due to Salmonella
4   Listeria        IQF Raspberries due to Listeria

本质上，我的分隔符是in、may contain和due to

example['hazard'] = example['title'].str.extract(r'^(.*?) in\b')
example['hazard'] = example['title'].str.extract(r'\b may contain (.*)$')
example['hazard'] = example['title'].str.extract(r'\b due to (.*)$')

我编写了上面的代码来测试每个分隔符，但希望在同一列中提取所有分隔符

我该怎么做

我感谢所有的帮助

Answer 1

您可以将分隔符连接到列表中，并通过"|".join将它们连接起来，以将其转换为更大的模式。从那里，Series.str.extract可以得到所有匹配项，我们重新调整形状以匹配原始大小

seperators = [r"^(.*?) in\b", r"\b may contain (.*)$", r"\b due to (.*)$"]
sep_pattern = r"|".join(seperators)

example["hazard"] = (example["title"].str.extract(sep_pattern)
                       .stack()
                       .droplevel(1))

print(example)
                                          title           hazard
0                   Undeclared milk in Burnbrae  Undeclared milk
1             Undeclared milk in certain Bumble  Undeclared milk
2  Certain cheese products may contain listeria         listeria
3        Ocean brand recalled due to Salmonella       Salmonella
4               IQF Raspberries due to Listeria         Listeria

Answer 2

获得相同结果的更为首要原则的方法：

def func(s: str):
    check1 = re.search(r'^(.*?) in\b',s)
    check2 = re.search(r'\b may contain (.*)$',s)
    check3 = re.search(r'\b due to (.*)$',s)
    if check1:
        return check1.group(1)
    elif check2:
        return check2.group(1)
    elif check3:
        return check3.group(1)
    else:
        return np.nan

example["hazard"] = example["title"].apply(func)