Python3.x 根据另一列值对多个数据框列进行分组

我有一个数据框:

    refid   col2    price1  factor1 price2  factor2 price3  factor3
  0   1       a      200       1      180     3     150       10
  1   2       b      500       1      450     3     400       10
  2   3       c      700       1      620     2     550        5

我需要得到这个输出:

   refid    col2    price   factor
0   1        a      200       1
1   1        b      500       1
2   1        c      700       1
3   2        a      180       3
4   2        b      450       3
5   2        c      620       2
6   3        a      150       10
7   3        b      400       10
8   3        c      550       5

现在我正在try 使用df.熔化方法，但无法使其工作，这是代码和当前结果:

df2_melt = df2.melt(id_vars=["refid","col2"],
        value_vars=["price1","price2","price3",
                   "factor1","factor2","factor3"],
        var_name="Price", 
        value_name="factor")



    refid   col2    price   factor
0       1   a      price1   200
1       2   b      price1   500
2       3   c      price1   700
3       1   a      price2   180
4       2   b      price2   450
5       3   c      price2   620
6       1   a      price3   150
7       2   b      price3   400
8       3   c      price3   550
9       1   a      factor1  1
10      2   b      factor1  1
11      3   c      factor1  1
12      1   a      factor2  3
13      2   b      factor2  3
14      3   c      factor2  2
15      1   a      factor3  10
16      2   b      factor3  10
17      3   c      factor3  5