I need some help on making an animated plot using Matplotlib

Question

I have an array x_trj that has shape (50,12), and I would like to make an animation for all the rows corresponding to certain columns in a 2-D plot (so I can see what direction each line is going). Below is my code:

from matplotlib.animation import FuncAnimation

fig,ax = plt.subplots()

# Plot initial line to fill in as we go
line, = ax.plot([], [], lw=2)

def init():
    line.set_data([], [])
    return line,

def animate(i):
    # Plot resulting trajecotry of car
    
    line.set_xdata(x_trj[i,0:9:4])
  

    line.set_ydata(x_trj[i,1:10:4])
   

    return line,


anim = FuncAnimation(fig, animate, init_func = init, frames=x_trj.shape[0], interval=200) # animation doesn't show up?

However, the animation does not show up at all. All I get is an empty figure. How should I fix this issue? I am writing my code in Google colab. The animation shows up but it's empty (it has a built-in play button):

Answer 1

I don't know what values you have in x_traj but I had to set xlim, ylim to see animation because animation doesn't change visible area automatically and it displays line in area which I can see.

I tested it only on local computer.

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

np.random.seed(0)  # `randint()` will always select the same values
x_trj = np.random.randint(0, 10, (52,12))

fig, ax = plt.subplots()
ax.set_xlim(0, 10)  # it would need to get min(), max() values from x_trj
ax.set_ylim(0, 10)  # it would need to get min(), max() values from x_trj

#ax = plt.axes(xlim=(0, 10), ylim=(0, 10))  # needs `ax =`

line, = ax.plot([], [], lw=2)

def init():
    line.set_data([], [])
    return line,

def animate(i):
    print('i:', i)

    x = x_trj[i,0:9:4]
    y = x_trj[i,1:10:4]
    print('x,y:', x, y)

    line.set_xdata(x)
    line.set_ydata(y)

    return line,

anim = FuncAnimation(fig, animate, init_func=init, frames=x_trj.shape[0], interval=200)

plt.show()

---

Eventually you can change xlim, ylim during animation to change visible area but this may not look as you expect.

def animate(i):
    print('i:', i)

    x = x_trj[i,0:9:4]
    y = x_trj[i,1:10:4]
    print('x,y:', x, y)

    line.set_xdata(x)
    line.set_ydata(y)

    ax.set_xlim(min(x), max(x))  # change visible are
    ax.set_ylim(min(y), max(y))  # change visible are

    return line,