matplotlib.lines.VertexSelector class in Python

Last Updated : 20 Aug, 2021

The matplotlib.lines.VertexSelector class belongs to the matplotlib.lines module. The matplotlib.lines module contains all the 2D line class that can be drawn with a variety of line styles, markers, and colors. matplotlib.lines.VertexSelector class is used to for managing the callbacks that maintain a list of selected vertices for matplotlib.lines.Line2D. The process_selected() function gets overridden by the derived classes for the picks.

Syntax: class matplotlib.lines.VertexSelector(line)
Parameter:

lines: These represent the lines that are defined for the plotting.

Methods of the class:

onpick(self, event): The selected set of indices gets updated when the line is picked using this method.
process_selected(self, ind, xs, ys): By default it does the implementation of "do nothing" of the process_selected() method. The 'ind' represents the indices of the selected vertices whereas 'xs' and 'ys' are the coordinates of the selected vertices.

Example #1:

Python3

import numpy as np
import matplotlib.pyplot as plt
import matplotlib.lines as lines


# class for highlighting selected area
class Highlighter(lines.VertexSelector):
    
    # constructor for the highlighter class
    def __init__(self, line, fmt ='ro', **kwargs):
        lines.VertexSelector.__init__(self, line)
        self.markers, = self.axes.plot([], [], fmt, **kwargs)
    
    # helper function process selected area and plot graph accordingly
    def process_selected(self, ind, xs, ys):
        self.markers.set_data(xs, ys)
        self.canvas.draw()

figure, ax = plt.subplots()
x_axis, y_axis = np.random.rand(2, 30)
line, = ax.plot(x_axis, y_axis, 'bs-', picker = 5)

selector = Highlighter(line)
plt.show()

Output:

Example 2:

Python3

import matplotlib.pyplot as plt
import matplotlib.lines as lines
from matplotlib.collections import PathCollection

lines.VertexSelector

# class for plot clicked area
class dragged_lines:
    
     # constructor for the dragged_lines class
    def __init__(self, ax):
        self.ax = ax
        self.c = ax.get_figure().canvas

        self.line = lines.Line2D(x, y, picker = 5, marker ='o',
                              markerfacecolor ='g', color ='y')

        self.ax.add_line(self.line)
        self.c.draw_idle()
        self.sid = self.c.mpl_connect('pick_event', self.lineclicker)

    def lineclicker(self, event):
        if event.artist:
            print("line selected ", event.artist)
            self.follower = self.c.mpl_connect("motion_notify_event",
                                                 self.mouse_follower)
            self.releaser = self.c.mpl_connect("button_press_event", 
                                            self.release_after_click)

    def mouse_follower(self, event):
        self.line.set_data([event.xdata, event.ydata])
        self.c.draw_idle()

    def release_after_click(self, event):
        data = self.line.get_data()
        print(data)

        self.c.mpl_disconnect(self.releaser)
        self.c.mpl_disconnect(self.follower)

figure = plt.figure()
axes = figure.add_subplot(111)
x_axis, y_axis = [2, 4, 5, 7], [8, 6, 12, 9]
axes.plot(x_axis, y_axis)
Vline = dragged_lines(axes)
plt.show()