"""

=============

Span Selector

=============

The `.SpanSelector` is a mouse widget that enables selecting a range on an

axis.

Here, an x-range can be selected on the upper axis; a detailed view of the

selected range is then plotted on the lower axis.

.. note::

If the SpanSelector object is garbage collected you will lose the

interactivity. You must keep a hard reference to it to prevent this.

"""

import numpy as np

import matplotlib.pyplot as plt

from matplotlib.widgets import SpanSelector

# Fixing random state for reproducibility

np.random.seed(19680801)

fig, (ax1, ax2) = plt.subplots(2, figsize=(8, 6))

x = np.arange(0.0, 5.0, 0.01)

y = np.sin(2 * np.pi * x) + 0.5 * np.random.randn(len(x))

ax1.plot(x, y)

ax1.set_ylim(-2, 2)

ax1.set_title('Press left mouse button and drag '

'to select a region in the top graph')

line2, = ax2.plot([], [])

def onselect(xmin, xmax):

indmin, indmax = np.searchsorted(x, (xmin, xmax))

indmax = min(len(x) - 1, indmax)

region_x = x[indmin:indmax]

region_y = y[indmin:indmax]

if len(region_x) >= 2:

line2.set_data(region_x, region_y)

ax2.set_xlim(region_x[0], region_x[-1])

ax2.set_ylim(region_y.min(), region_y.max())

fig.canvas.draw_idle()

span = SpanSelector(

ax1,

onselect,

"horizontal",

useblit=True,

props=dict(alpha=0.5, facecolor="tab:blue"),

interactive=True,

drag_from_anywhere=True

)

# Set useblit=True on most backends for enhanced performance.

plt.show()

#############################################################################

#

# .. admonition:: References

#

# The use of the following functions, methods, classes and modules is shown

# in this example:

#

# - `matplotlib.widgets.SpanSelector`