python-3.x - 将绘图的两个点与另一条线连接起来

Question

我想将数据框图中的两个点与另一条线连接起来，并将其添加到图中:

import numpy as np
from numpy.random import randn
import pandas as pd
from datetime import datetime
import matplotlib.pyplot as plt
%matplotlib inline
days = [datetime(2016, 1, 1), datetime(2016, 1, 2),datetime(2016, 1, 3),datetime(2016, 1, 4)]
dt_ind = pd.DatetimeIndex(days)
data = np.random.randn(4,2)
cols = ['A','B']
df = pd.DataFrame(data,dt_ind,cols)
df['A'].plot(figsize=(12,4), sort_columns=True)

这是数据框:
enter image description here

和情节:
enter image description here

这怎么可能？例如添加一条从点 2 到点 4(或任意两点)的线

Answer 1

您想使用 matplotlib 的 plt.subplots() 函数返回一个 fig 和 ax 对象，这样您就可以向 ax 添加单独的行。

import numpy as np
from numpy.random import randn
import pandas as pd
from datetime import datetime
import matplotlib.pyplot as plt
%matplotlib inline
days = [datetime(2016, 1, 1),
        datetime(2016, 1, 2), 
        datetime(2016, 1, 3), 
        datetime(2016, 1, 4)]

dt_ind = pd.DatetimeIndex(days)
data = np.random.randn(4,2)
cols = ['A','B']
df = pd.DataFrame(data,dt_ind,cols)


fig, ax = plt.subplots()
ax.plot(df['A'], color='red')
ax.plot([df.index[1], df.index[3]],
        [df['A'][1], df['A'][3]], color='blue')