我有这个数据框：
key variable value
0 0.25 -0.2 606623.455859
1 0.27 -0.2 621462.029200
2 0.30 -0.2 640299.078053
3 0.33 -0.2 653686.910706
4 0.35 -0.2 659278.593742
5 0.37 -0.2 665684.466383
6 0.40 -0.2 671975.695814
7 0.25 0 530091.733402
8 0.27 0 542501.852937
9 0.30 0 557799.179433
10 0.33 0 571140.149887
11 0.35 0 575117.783803
12 0.37 0 582709.048163
13 0.40 0 588168.965913
14 0.25 0.2 466275.721535
15 0.27 0.2 478678.452615
16 0.30 0.2 492749.041489
17 0.33 0.2 500792.917910
18 0.35 0.2 503620.638204 …