How to select area within a plot (Python) and extract the data within the area

Question

I am currently working with a dataset that includes signals with a duration of around 10 seconds and a sampling time of 0.1 seconds. My goal is to extract a specific part of this data and save it into a python dictionary. The relevant part is about 4 seconds long.

Ideally this is what I would like to do:

1. Plot the whole 10 seconds of data.

2. Mark the relevant part of the signals for example with a bounding box.

3. Extract the data within the bounding box after closing the plot window or pushing a button.

4. Go back to 1. and take new data.

I saw that matplotlib has the ability to draw patches and extract the data points within the patch. Is it maybe possible to add a patch to the plot after the plot was created (after the plt.show() command was executed)?

Thank you in advance and best regards,

Manuel

Answer 1

You may use a SpanSelector.

You basically only need to add a line for saving to the matplotlib example.

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

fig = plt.figure(figsize=(8, 6))
ax = fig.add_subplot(211)

x = np.arange(0.0, 5.0, 0.01)
y = np.sin(2*np.pi*x) + 0.5*np.random.randn(len(x))

ax.plot(x, y, '-')
ax.set_ylim(-2, 2)
ax.set_title('Press left mouse button and drag to test')

ax2 = fig.add_subplot(212)
line2, = ax2.plot(x, y, '-')


def onselect(xmin, xmax):
    indmin, indmax = np.searchsorted(x, (xmin, xmax))
    indmax = min(len(x) - 1, indmax)

    thisx = x[indmin:indmax]
    thisy = y[indmin:indmax]
    line2.set_data(thisx, thisy)
    ax2.set_xlim(thisx[0], thisx[-1])
    ax2.set_ylim(thisy.min(), thisy.max())
    fig.canvas.draw_idle()

    # save
    np.savetxt("text.out", np.c_[thisx, thisy])

# set useblit True on gtkagg for enhanced performance
span = SpanSelector(ax, onselect, 'horizontal', useblit=True,
                    rectprops=dict(alpha=0.5, facecolor='red'))

plt.show()