壓扁多指標大熊貓數據幀，其中列名成爲價值

Question

讓我們說，我有以下DF：

import pandas as pd 
df = pd.DataFrame(data={'Status' : ['green','green','red','blue','red','yellow','black'], 
'Group' : ['A','A','B','C','A','B','C'], 
'City' : ['Toronto','Montreal','Vancouver','Toronto','Edmonton','Winnipeg','Windsor'], 
'Sales' : [13,6,16,8,4,3,1]}) 
df.drop('Status',axis=1,inplace=True) 
ndf = pd.pivot_table(df,values=['Sales'],index=['City'],columns=['Group'],fill_value=0,margins=False) 

結果看起來是這樣的：

In [321]: ndf 
Out[321]: 
      Sales 
Group   A B C 
City 
Edmonton  4 0 0 
Montreal  6 0 0 
Toronto  13 0 8 
Vancouver  0 16 0 
Windsor  0 0 1 
Winnipeg  0 3 0 

我怎樣才能將其壓平，使得它變成了一個單層數據框，但有一列指定組？

即，結果應該是：

City group sales 
Edmonton A 4 
Edmonton B 0 
Edmonton C 0 
Montreal A 6 
Montreal B 0 
Montreal C 0 
Toronto  A 13 
Toronto  B 0 
Toronto  C 8 
Vancouver A 0 
Vancouver B 16 
Vancouver C 0 
Windsor  A 0 
Windsor  B 0 
Windsor  C 1 
Winnipeg A 0 
Winnipeg B 3 
Winnipeg C 0 

Answer 1

使用stack和reset_index

In [1260]: ndf.stack().reset_index() 
Out[1260]: 
     City Group Sales 
0 Edmonton  A  4 
1 Edmonton  B  0 
2 Edmonton  C  0 
3 Montreal  A  6 
4 Montreal  B  0 
5 Montreal  C  0 
6  Toronto  A  13 
7  Toronto  B  0 
8  Toronto  C  8 
9 Vancouver  A  0 
10 Vancouver  B  16 
11 Vancouver  C  0 
12 Windsor  A  0 
13 Windsor  B  0 
14 Windsor  C  1 
15 Winnipeg  A  0 
16 Winnipeg  B  3 
17 Winnipeg  C  0 

Answer 2

這是很容易實現的，例如：

ndf.stack().reset_index() 

     City Group Sales 
0 Edmonton  A  4 
1 Edmonton  B  0 
2 Edmonton  C  0 
3 Montreal  A  6 
4 Montreal  B  0 
5 Montreal  C  0 
6  Toronto  A  13 
7  Toronto  B  0 
8  Toronto  C  8 
9 Vancouver  A  0 
10 Vancouver  B  16 
11 Vancouver  C  0 
12 Windsor  A  0 
13 Windsor  B  0 
14 Windsor  C  1 
15 Winnipeg  A  0 
16 Winnipeg  B  3 
17 Winnipeg  C  0