Pythonfor循环来更新数据帧

Question

我正在尝试重新创建一个使用Python的VBA宏。有谁能告诉我我应该用的是哪种表达方式，以便得到低于预期的结果？非常感谢。

档案1：

Product Colour  Price
Book    NaN 5
Table   NaN 10
Chair   NaN 7

档案2：

Colour 
Blue 
Red 
Green

循环后的预期结果(文件1)：

Product Colour Price    
Book    Blue    5
Table   Blue    10
Chair   Blue    7
Book    Red 5
Table   Red 10
Chair   Red 7
Book    Green   5
Table   Green   10
Chair   Green   7

Answer 1

首先根据df1的长度复制df2值，然后将list comprehesion和chain用于Colour，如下所示：

from itertools import chain


df = pd.DataFrame({'Product': df1['Product'].values.tolist()*len(df2),
                   'Price'  : df1['Price'].values.tolist()*len(df2),
                   'Colour' : list(chain.from_iterable([[v]*len(df1) for v in df2['Colour'].values.tolist()]))})

print(df)
  Product  Price Colour
0    Book      5   Blue
1   Table     10   Blue
2   Chair      7   Blue
3    Book      5    Red
4   Table     10    Red
5   Chair      7    Red
6    Book      5  Green
7   Table     10  Green
8   Chair      7  Green

Answer 2

您可以使用列表理解，类似于嵌套的for循环：

df = pd.DataFrame([[product, colour, price] for colour in df2['Colour'] \
                   for product, price in zip(df1['Product'], df1['Price'])],
                  columns=['Product', 'Colour', 'Price'])

print(df)

  Product Colour  Price
0    Book   Blue      5
1   Table   Blue     10
2   Chair   Blue      7
3    Book    Red      5
4   Table    Red     10
5   Chair    Red      7
6    Book  Green      5
7   Table  Green     10
8   Chair  Green      7