Matplotlib – Cursor Widget

Matplotlib is a Data Visualization library in python. It consists of many widgets that are designed to work for any of the GUI backends. Some examples of widgets in matplotlib are Button, CheckButtons, RadioButtons, Cursor, and TextBox. In this article, the Cursor Widget of Matplotlib library has been discussed.

A Cursor spans the axes horizontally and/or vertically and moves with the mouse cursor. 

Syntax: Cursor(ax, horizOn=True, vertOn=True, useblit=False, **lineprops)

Parameters:

• ax : Axes to attach the cursor to.
• Optional Parameters:
• horizOn : To draw the horizontal line(default: True).
• vertOn : To draw the vertical line(default: True).
• useblit : Use blitting for faster drawing if supported by the backend(default: False).
• **lineprops: Line properties to control appearance of the lines(linewidth, color).

Example 1:

Python3

# importing cursor widget from matplotlib
from matplotlib.widgets import Cursor
import matplotlib.pyplot as plt
import numpy as np

fig = plt.figure()
ax = fig.add_axes([0.1, 0.1, 0.8, 0.8])

num = 100
x = np.random.rand(num)
y = np.random.rand(num)

ax.scatter(x, y, c='blue')
ax.set_xlabel('X-axis')
ax.set_ylabel('Y-axis')

cursor = Cursor(ax, color='green', linewidth=2)
plt.show()

Output:

In the above output, the cursor can be moved horizontally and vertically throughout the matplotlib axes. We can just drag the cursor wherever necessary.

MultiCursor

MultiCursor is used to show cursor on multiple plots at the same time i.e., Cursor is shared between multiple axes.

Syntax:

MultiCursor(canvas, axes, useblit=True, horizOn=False, vertOn=True, **lineprops)

Example:

Python3

# Import MultiCursor from matplotlib
from matplotlib.widgets import MultiCursor
import matplotlib.pyplot as plt
import numpy as np

fig, (ax1, ax2) = plt.subplots(nrows=2, sharex=True)

x = np.linspace(-np.pi, np.pi, 256, endpoint=True)
y = np.sin(x)
z = np.cos(x)

ax1.plot(x, y, label="sin function")
ax1.legend(loc="upper right")
ax2.plot(x, z, label="cos function")

multi = MultiCursor(fig.canvas, (ax1, ax2), color='g', lw=2,
                    horizOn=False, vertOn=True)

ax2.legend(loc="upper right")
plt.show()

Output:

Example:

Python3

from matplotlib.widgets import MultiCursor
import matplotlib.pyplot as plt
import numpy as np

fig, (ax1, ax2) = plt.subplots(1, 2, figsize=(12, 5))

x1 = ['Telugu', 'Hindi', 'English',
      'Maths', 'Science', 'Social']
y1 = [45, 34, 30, 45, 50, 38]
y2 = [36, 28, 30, 45, 38, 50]

labels = ["in 2020", "in 2021"]

l1 = ax1.plot(x1, y1, 'o', color="green")
l2 = ax2.plot(x1, y2, 'o', color="blue")

ax1.set_yticks(np.arange(0, 51, 5))
ax2.set_yticks(np.arange(0, 51, 5))

ax1.set_ylabel('Number of students passed', fontsize=15)

fig.legend([l1, l2], labels=labels, loc="upper right")
cursor = MultiCursor(fig.canvas, (ax1, ax2), color='r',
                     lw=2, horizOn=True, vertOn=True)

plt.subplots_adjust(right=0.9)
plt.show()

Output: