在此代码中，我绘制了pct_day。由于该值不会像股票值那样增加，因此可以绘制此数据，将要绘制的当前值添加到先前的值，然后绘制该数据。这样，折线图会随时间增加，而不是下面的图表在零线上绘制的图？
High Low Open Close Volume Adj Close year pct_day
month day
1 2 794.913004 779.509998 788.783002 789.163007 6.372860e+08 789.163007 1997.400000 0.002211
3 833.470005 818.124662 823.937345 828.889339 9.985193e+08 828.889339 1997.866667 0.004160
4 863.153573 849.154299 858.737861 853.571429 1.042729e+09 853.571429 1997.714286 -0.003345
5 900.455715 888.571429 895.716426 894.472137 1.022023e+09 894.472137 1998.357143 -0.001216
6 847.453076 837.161537 840.123847 844.383843 8.889831e+08 844.383843 1998.076923 0.003679
... ... ... ... ... ... ... ... ... ...
12 27 909.735997 900.942000 905.528664 904.734009 7.485793e+08 904.734009 1998.133333 -0.000308
28 946.635010 940.440016 942.995721 944.127147 7.552150e+08 944.127147 1998.071429 0.001251
29 950.723837 941.625390 944.760775 947.200773 6.830400e+08 947.200773 1998.076923 0.002899
30 891.501671 883.954989 887.031665 887.819181 6.010675e+08 887.819181 1997.833333 0.001844
31 918.943857 910.320763 916.251549 913.786154 6.879523e+08 913.786154 1997.923077 -0.002772
363 rows × 8 columns
如下所示：
