Matplotlib 指示 X 和 Y 轴上的点 [英] Matplotlib Indicate Point on X and Y Axis

问题描述

我经常想使用 matplotlib 沿曲线突出显示一个点，以绘制如下所示的图:

I often want to highlight a point along a curve using matplotlib to make a plot that looks like:

以下代码用于创建图

import numpy as np
import matplotlib.pyplot as plt
import seaborn as sns

y  = np.array([0,5,10,15,20,25,30,35,40,45,50,55,60,65,70,75,80,85,90,95,100])/100.
x = 100. - np.array([
    99.79,98.96,98.65,98.39,98.13,97.88,97.61,97.33,97.01,96.65,96.21,
    95.72,95.16,94.46,93.52,92.31,90.66,88.48,84.04,79.34,19.32])
ax = plt.subplot(111)
line = plt.plot(x,y)


def highlight_point(ax,line,point,linestyle=':'):
    c = line.get_color()
    xmin = ax.get_xlim()[0]
    ymin = ax.get_ylim()[0]

    ax.plot([xmin,point[0]],[point[1],point[1]],color=c,linestyle=linestyle)
    ax.plot([point[0],point[0]],[ymin,point[1]],color=c,linestyle=linestyle)

plt.xlim([0,85])
plt.ylim([0,1])
highlight_point(ax,line[0],[x[10],y[10]])
plt.show()

当无法输入 xlim 和 ylim 或稍后在图中添加了另一个图形时，上述方法将失败.我想使用 axhline 或 hlines 的某种组合，在这些组合中我可以将图的左/底指定到某个数学点.

The above method fails when the xlim and ylim are failed to be entered or if another plot were added to the figure later. I would like some combination of axhline or hlines where I can specify the left/bottom of the plot to a certain mathematical point.

推荐答案

一种解决方法是，每次重新绘制画布时都更新行.为此，我们可以使用连接到 draw_event 侦听器的更新方法创建一个 PointMarkers 类.这样，不仅可以在创建标记线之后添加点，还可以在调整画布大小或平移画布时添加线.

A way to go could be to update the lines each time the canvas gets redrawn. To this end we could create a class PointMarkers with an update method that is connected to the draw_event listener. This way the lines will update not only if points are added after the marker lines' creation, but also when the canvas is resized or panned.

import numpy as np
import matplotlib.pyplot as plt
import seaborn as sns

class PointMarker():
    def __init__(self, ax, point, **kwargs):
        self.ax = ax
        self.point = point
        if "line" in kwargs:
            self.c = kwargs.get("line").get_color()
        else:
            self.c = kwargs.get("color", "b")
        self.ls=kwargs.get("linestyle", ':')
        self.vline, = self.ax.plot([],[],color=self.c,linestyle=self.ls)
        self.hline, = self.ax.plot([],[],color=self.c,linestyle=self.ls)
        self.draw()

    def draw(self):
        xmin = ax.get_xlim()[0]
        ymin = ax.get_ylim()[0]
        self.vline.set_data([self.point[0], self.point[0]], [ymin,self.point[1]])
        self.hline.set_data([xmin, self.point[0]], [self.point[1], self.point[1]])

class PointMarkers():
    pointmarkers = []
    def add(self,ax, point, **kwargs ):
        pm = PointMarker(ax, point, **kwargs)
        self.pointmarkers.append(pm)
    def update(self, event=None):
        for pm in self.pointmarkers:
            pm.draw()

x = np.arange(1,17)
y = np.log(x)
ax = plt.subplot(111)
line = plt.plot(x,y)

# register the markers
p = PointMarkers()
p.add(ax,[x[5],y[5]], line=line[0])
p.add(ax,[x[12],y[12]], color="purple", linestyle="-.")
# connect event listener
cid = plt.gcf().canvas.mpl_connect("draw_event", p.update)

#testing: draw some new points or change axis limits
plt.plot([5,11],[-0.5,0.6])
#plt.xlim([0,85])
#plt.ylim([0,1])

plt.show()

为了保存，重绘需要在save命令之前直接手动执行，如

For saving, the redrawing would need to be performed manually directly before the save command, like

plt.gcf().canvas.draw()
plt.savefig(...)

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