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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)

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

Methods of the class: 

  1. onpick(self, event): The selected set of indices gets updated when the line is picked using this method.
  2. 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:  


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)
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)


Example 2: 


import matplotlib.pyplot as plt
import matplotlib.lines as lines
from matplotlib.collections import PathCollection
# class for plot clicked area
class dragged_lines:
     # constructor for the dragged_lines class
    def __init__(self, ax): = ax
        self.c = ax.get_figure().canvas
        self.line = lines.Line2D(x, y, picker = 5, marker ='o',
                              markerfacecolor ='g', color ='y')

        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.releaser = self.c.mpl_connect("button_press_event",
    def mouse_follower(self, event):
        self.line.set_data([event.xdata, event.ydata])
    def release_after_click(self, event):
        data = self.line.get_data()
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)



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