如何删除结果pos_tag中的方括号

Question

我想从数据框中提取名词。我这样做

import pandas as pd
import nltk
from nltk.tag import pos_tag
df = pd.DataFrame({'pos': ['noun', 'Alice', 'good', 'well', 'city']})
noun=[]
for index, row in df.iterrows():
    noun.append([word for word,pos in pos_tag(row) if pos == 'NN'])
df['noun'] = noun  

我得到了df ['noun']

0     [noun]
1    [Alice]
2         []
3         []
4     [city]

我使用正则表达式

df['noun'].replace('[^a-zA-Z0-9]', '', regex = True)

再次

0     [noun]
1    [Alice]
2         []
3         []
4     [city]
Name: noun, dtype: object

出了什么问题？

Answer 1

括号表示您在数据框的每个单元格中都有列表。如果您确定每个列表中最多只有一个元素，则可以在名词列上使用str并提取第一个元素：

df['noun'] = df.noun.str[0]

df
#    pos    noun
#0  noun    noun
#1  Alice   Alice
#2  good    NaN
#3  well    NaN
#4  city    city