如何转换这样的数据框:
a b c
0 1.067683 -1.110463 0.208670
1 -1.321405 0.368915 -1.055342
2 -0.807333 0.082980 -0.873361
进入
det value
0 a 1.067683
1 a -1.321405
2 a -0.807333
3 b -1.110463
4 b 0.368915
5 b 0.082980
6 b 0.082980
7 c 0.208670
8 c -1.055342
9 c -0.873361