Remove Points / Lines Canvas Python Matplotlib

Question

i use the following Code to draw lines in matplotlib with mouse Event. Every click they save the coordinates and draw lines.

from matplotlib import pyplot as plt

class LineBuilder:
def __init__(self, line):
    self.line = line
    self.xs = list(line.get_xdata())
    self.ys = list(line.get_ydata())
    self.cid = line.figure.canvas.mpl_connect('button_press_event', self)
def __call__(self, event):
    if event.inaxes!=self.line.axes: return
    self.xs.append(event.xdata)
    self.ys.append(event.ydata)
    self.line.set_data(self.xs, self.ys)
    self.line.figure.canvas.draw_idle()
    print(self.xs)
    print(self.ys)

fig = plt.figure()
ax = fig.add_subplot(111)
ax.set_title('click to build line segments')
line, = ax.plot([0], [0], marker="o", linestyle="") 
linebuilder = LineBuilder(line)
plt.show()

Is it possible to delete same lines? For example if my Point 2 are not on the right position, then i would like delete the complete lines and points.

How can I do this??

Right leg Right leg · Accepted Answer · 2019-09-06T09:11:15

Since you're building an interaction that's more complex than simply creating a point where the user clicked, I suggest that you use a button.

You need to define exactly what action you want to implement: remove the last point, remove all the points, remove all the points but the ones that were used for initialization...

I'm gonna show you how you can create a Reset button that will remove all the points, based upon this example from Matplotlib's doc.

First, create an Axes object that your button will fill. You'll want to adjust the main ax so the two don't overlap.

from matplotlib.widgets import Button

plt.subplots_adjust(bottom=0.2)
breset_ax = plt.axes([0.7, 0.05, 0.1, 0.075])
breset = Button(breset_ax, 'Reset')

Then you'll set the button's callback. I find it relevant to define that callback in the LineBuilder class, as it will clear the encapsulated points.

class LineBuilder:
    ...

    def reset(self, _event):
        self.xs = []
        self.ys = []
        self.line.set_data(self.xs, self.ys)
        self.line.figure.canvas.draw_idle()

Then, bind that callback to the button:

breset.on_clicked(linebuilder.reset)

This will give you something like that:

And clicking on the Reset button will remove all the points that have been drawn.

Complete code:

from matplotlib import pyplot as plt
from matplotlib.widgets import Button

class LineBuilder:
    def __init__(self, line):
        self.line = line
        self.xs = list(line.get_xdata())
        self.ys = list(line.get_ydata())
        self.cid = line.figure.canvas.mpl_connect('button_press_event', self)

    def __call__(self, event):
        if event.inaxes!=self.line.axes:
            return
        self.xs.append(event.xdata)
        self.ys.append(event.ydata)
        self.line.set_data(self.xs, self.ys)
        self.line.figure.canvas.draw_idle()
        print(self.xs)
        print(self.ys)

    def reset(self, _event):
        self.xs = []
        self.ys = []
        self.line.set_data(self.xs, self.ys)
        self.line.figure.canvas.draw_idle()

fig = plt.figure()
ax = fig.add_subplot(111)
ax.set_title('click to build line segments')
line, = ax.plot([0], [0], marker="o", linestyle="")
linebuilder = LineBuilder(line)

plt.subplots_adjust(bottom=0.2)
breset_ax = plt.axes([0.7, 0.05, 0.1, 0.075])
breset = Button(breset_ax, 'Reset')
breset.on_clicked(linebuilder.reset)

plt.show()

Remove Points / Lines Canvas Python Matplotlib

2 Answers