animated subplots using matplotlib

Question

I have this code. I want to add a subplot to draw the cosine function. (I do not want to create a class). The second plot should be dynamically updated as well

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

def data_gen():
    t = data_gen.t
    cnt = 0
    while cnt < 1000:
        cnt+=1
        t += 0.05
        yield t, np.sin(2*np.pi*t) * np.exp(-t/10.)
data_gen.t = 0

fig, ax = plt.subplots()
line, = ax.plot([], [], lw=2)
ax.set_ylim(-1.1, 1.1)
ax.set_xlim(0, 5)
ax.grid()
xdata, ydata = [], []
def run(data):
    # update the data
    t,y = data
    xdata.append(t)
    ydata.append(y)
    xmin, xmax = ax.get_xlim()

    if t >= xmax:
        ax.set_xlim(xmin, 2*xmax)
        ax.figure.canvas.draw()
    line.set_data(xdata, ydata)

    return line,

ani = animation.FuncAnimation(fig, run, data_gen, blit=True, interval=10,
    repeat=False)
plt.show()

Trenton McKinney · Accepted Answer · 2021-09-25 14:03:52Z

44

Basically you can use a very similar structure as the one you have in your example. You only need to create an additional axes (subplot) and a second line object:

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

def data_gen():
    t = data_gen.t
    cnt = 0
    while cnt < 1000:
        cnt+=1
        t += 0.05
        y1 = np.sin(2*np.pi*t) * np.exp(-t/10.)
        y2 = np.cos(2*np.pi*t) * np.exp(-t/10.)
        # adapted the data generator to yield both sin and cos
        yield t, y1, y2

data_gen.t = 0

# create a figure with two subplots
fig, (ax1, ax2) = plt.subplots(2,1)

# intialize two line objects (one in each axes)
line1, = ax1.plot([], [], lw=2)
line2, = ax2.plot([], [], lw=2, color='r')
line = [line1, line2]

# the same axes initalizations as before (just now we do it for both of them)
for ax in [ax1, ax2]:
    ax.set_ylim(-1.1, 1.1)
    ax.set_xlim(0, 5)
    ax.grid()

# initialize the data arrays 
xdata, y1data, y2data = [], [], []
def run(data):
    # update the data
    t, y1, y2 = data
    xdata.append(t)
    y1data.append(y1)
    y2data.append(y2)

    # axis limits checking. Same as before, just for both axes
    for ax in [ax1, ax2]:
        xmin, xmax = ax.get_xlim()
        if t >= xmax:
            ax.set_xlim(xmin, 2*xmax)
            ax.figure.canvas.draw()

    # update the data of both line objects
    line[0].set_data(xdata, y1data)
    line[1].set_data(xdata, y2data)

    return line

ani = animation.FuncAnimation(fig, run, data_gen, blit=True, interval=10,
    repeat=False)
plt.show()

edited Sep 25, 2021 at 14:03

Trenton McKinney

63.2k41 gold badges169 silver badges212 bronze badges

answered Apr 23, 2015 at 21:39

hitzg

12.8k57 silver badges55 bronze badges

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6 Comments

ZakS Over a year ago

could you explain the difference between line1, = ax1.plot([], [], lw=2) and line1 = ax1.plot([], [], lw=2) (second version missing comma)?

hitzg Over a year ago

ax1.plot returns a list of (potentially) multiple lines. With the comma, the first element of that list is assigned to line1. Without the comma line1 will contain the entire list.

Yograj Singh Mandloi Over a year ago

How to modify this one if y1 and y2 need to be drawn on the same subplot but the data_gen is a function with some input parameter k. So each subplot show for different values of k.

MattS Over a year ago

How to run this in jupyter notebook? adding %matplotlib inline doesn't work

Indivara Over a year ago

@MattS %matplotlib notebook

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