python - 在复制其他列数据的同时拆分一列中的行中的值

Question

我试图将列的每一行中的值拆分为多行，同时复制其他列的相应值。我是 python 的新手，正在尝试找出一种方法来将此解决方案实现到更大的数据集。

这是输入文件:

Name    Year    Subject                                        State
Jack    2003    Math, Sci, Music                               MA
Sam     2004    Math, PE, Language, Social                     CA
Nicole  2005    Math, Life Sci, Geography, Music, Computer Sci NY

这是我想要的输出:

Name    Year    Subject            State
Jack    2003    Math               MA
Jack    2003    Sci                MA
Jack    2003    Music              MA
Sam     2004    Math               CA
Sam     2004    PE                 CA
Sam     2004    Language           CA
Sam     2004    Social             CA
Nicole  2005    Math               NY
Nicole  2005    Life Sci           NY
Nicole  2005    Geography          NY
Nicole  2005    Music              NY
Nicole  2005    Computer Sci       NY

我试过这段代码:

import pandas as pd 

df= pd.read_csv('C:/Users/3216140/Desktop/test.csv', delimiter=',', skiprows = 1, names = ["Name","Year","Subject","State"] ) 
print(df) 
sub = df['Subject'].str.split(',').apply(pd.Series, 1).stack() 
sub.index = sub.index.droplevel(-1) 
sub.name = 'Subject' 
print (sub) 
del df['Subject'] 
df.join(sub) 
print(df) 

但是连接似乎没有起作用。我只是得到没有“主题”的输入文件作为输出。

Answer 1

你可以在这里使用np.repeat和itertools.chain。

from itertools import chain

v = df.pop('Subject').str.split(r'\s*,\s*')
df_new = pd.DataFrame(
    df.values.repeat(v.str.len(), axis=0),
    columns=df.columns
)
df_new['Subject'] = list(itertools.chain.from_iterable(v))

df_new

      Name State Year       Subject
0     Jack  2003   MA          Math
1     Jack  2003   MA           Sci
2     Jack  2003   MA         Music
3      Sam  2004   CA          Math
4      Sam  2004   CA            PE
5      Sam  2004   CA      Language
6      Sam  2004   CA        Social
7   Nicole  2005   NY          Math
8   Nicole  2005   NY      Life Sci
9   Nicole  2005   NY     Geography
10  Nicole  2005   NY         Music
11  Nicole  2005   NY  Computer Sci