如何在boxplot上绘制数据帧的最后值？

Question

我有一个2 * 4的方框图，每个方框包含21个方框。对于它们每个，我想绘制每个数据框列的最后一个值。

仔细研究其中一个：

fig,axes = plt.subplots(2, 4, figsize = (40,20))
deltas = np.arange(0.0, 1.05, 0.05)
l_stringss = [['call_this_month_', 'call_next_month_',   'call_this_quarter_','call_next_quarter_'],
          ['put_this_month_','put_next_month_', 'put_this_quarter_', 'put_next_quarter_']]

for l_strings in l_stringss:
    i = l_stringss.index(l_strings)
    for string in l_strings:
        j = l_strings.index(string)
        vol_dict = {}
        for delta in deltas:
            option = pd.read_csv(string + str(delta) + '.csv') 
            vol_dict[delta] = option.vol.values
        vols = pd.DataFrame(dict([(k,pd.Series(v)) for k, v in vol_dict.items()]))
        if 'call' in string:
            order = deltas
        elif 'put' in string:
            order = deltas[::-1]
        sns.boxplot(data = vols, order = order, ax = axes[i][j]).set_title(string[:-1])

输入数据示例：

     date        id       strike    vol     delta
0  2015-03-24  10000097     2.8  0.441618  0.005203
1  2015-03-25  10000097     2.8  0.013609  0.008506
2  2015-04-20  10000175     3.4  0.564792  0.015379
3  2015-04-21  10000167     3.3  0.366533  0.005255
4  2015-04-22  10000175     3.4  0.003894  0.021423