[Python] Python 3 - matplotlib - set_xdata/set_ydata not working

I try to display sensor data using set_xdata/set_ydata instead of plot so it refreshes faster

I found this tutorial

Problem: nothing shows up

Expected: I should see the plotted data (used to work with ax1.plot)

import pprint
import matplotlib.pyplot as plt
import matplotlib.animation as animation
import time
from matplotlib.widgets import Button # Import Button

fig,ax1 = plt.subplots(figsize=(10, 8))

# Initialize the plot lines with some dummy data
line1, = ax1.plot([0], [0], label="LEFT", color="gray")
line2, = ax1.plot([0], [0], label="RIGHT", color="gray")
line3, = ax1.plot([0], [0], label="LEFT smoothed", color="red")
line4, = ax1.plot([0], [0], label="RIGHT smoothed", color="green")

plt.title("Phil VL53L0X sensors", fontsize=20)

# setting x-axis label and y-axis label
plt.xlabel("time")
plt.ylabel("distance")

xarr = []
yarr1 = []
yarr2 = []
yarr1_s = []
yarr2_s = []
count = 0

WINDOW_SIZE = 10
MIN_DISTANCE = 20

# Create the button to clear data
def clear_data(event):
global xarr, yarr1, yarr2, count, yarr1_s, yarr2_s
xarr.clear()
yarr1.clear()
yarr2.clear()
yarr1_s.clear()
yarr2_s.clear()
count = 0
ax1.clear()
ax1.set_xlabel("Time")
ax1.set_ylabel("Distance (mm)")
ax1.legend()
plt.draw()

def animate(i):
global count

# faking data, this is usually read by a sensor returning values between 0 and 100
distance1 = count
distance2 = count

distance1 = distance1 - MIN_DISTANCE
if distance1 < 0:
distance1 = 0
distance2 = distance2 - MIN_DISTANCE
if distance2 < 0:
distance2 = 0

count += 1

# Append new data
xarr.append(count)
yarr1.append(distance1)
yarr2.append(distance2)

# Apply moving average
smoothed_distance1 = moving_average(yarr1)
smoothed_distance2 = moving_average(yarr2)

yarr1_s.append(smoothed_distance1)
yarr2_s.append(smoothed_distance2)

# Limit size of arrays to avoid excessive memory usage
if len(yarr1) > 100:
yarr1.pop(0)
yarr2.pop(0)
yarr1_s.pop(0)
yarr2_s.pop(0)
xarr.pop(0)

pprint.pprint(xarr)
pprint.pprint(yarr1)

# Update the X data (only once)
line1.set_xdata(xarr)
line2.set_xdata(xarr)
line3.set_xdata(xarr)
line4.set_xdata(xarr)

# Update the plot (without clearing it)
line1.set_ydata(yarr1)
line2.set_ydata(yarr2)
line3.set_ydata(yarr1_s)
line4.set_ydata(yarr2_s)

# Update the plot (this works)
#ax1.plot(xarr, yarr1, label="LEFT", color="gray")
#ax1.plot(xarr, yarr2, label="RIGHT", color="gray")
#ax1.plot(xarr, yarr1_s, label="LEFT s", color="red")
#ax1.plot(xarr, yarr2_s, label="RIGHT s", color="green")

fig.canvas.draw()
fig.canvas.flush_events()
time.sleep(0.1)


ani = animation.FuncAnimation(fig, animate, interval=1) # Increased interval for smoother updates

# Add a button to clear data
ax_button = plt.axes([0.8, 0.05, 0.1, 0.075])
btn = Button(ax_button, "Clear Data")
btn.on_clicked(clear_data)

plt.show()


I pprint the data as it animates, it is clearly there.

What am I missing here?



Continue reading...