Animating p9 figures using ArtistAnimation class of matplotlib

[gokceneraslan]

Hi,

I'm trying to make animations using p9 figures, but I end up with matplotlib exceptions. I was wondering whether there is a convenient way to make animations out of plotnine plots.

Here is what I've tried so far:

from plotnine import *
from plotnine.data import *

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

def plot1(y):
    return plt.scatter(y[:, 0], y[:, 1], c='black'),

def plot2(y):
    return (qplot(y[:, 0], y[:, 1], xlab='x', ylab='y') +
            theme_minimal()).draw(),

# Use mtcars as toy data
X = mtcars[['disp', 'hp']].as_matrix()

# Add little noise to make animation cool
data = [X+np.random.normal(0, 1, (X.shape[0], X.shape[1])) for _ in range(50)]

fig = plt.figure(figsize=(8, 8))
artists = [plot1(x) for x in data]
ani = ArtistAnimation(fig, artists, interval=100, repeat_delay=500)
ani.save('/tmp/animation.mp4')

fig = plt.figure(figsize=(8, 8))
artists = [plot2(x) for x in data]
ani = ArtistAnimation(fig, artists, interval=100, repeat_delay=500)
ani.save('/tmp/animation2.mp4')

Here is the exception I get:

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-39-98cef8b8381e> in <module>()
     25 artists = [plot2(x) for x in data]
     26 ani = ArtistAnimation(fig, artists, interval=100, repeat_delay=500)
---> 27 ani.save('/tmp/animation2.mp4')

~/.miniconda3/lib/python3.6/site-packages/matplotlib/animation.py in save(self, filename, writer, fps, dpi, codec, bitrate, extra_args, metadata, extra_anim, savefig_kwargs)
   1055                 for anim in all_anim:
   1056                     # Clear the initial frame
-> 1057                     anim._init_draw()
   1058                 for data in zip(*[a.new_saved_frame_seq()
   1059                                   for a in all_anim]):

~/.miniconda3/lib/python3.6/site-packages/matplotlib/animation.py in _init_draw(self)
   1374         # Flush the needed figures
   1375         for fig in figs:
-> 1376             fig.canvas.draw_idle()
   1377 
   1378     def _pre_draw(self, framedata, blit):

AttributeError: 'NoneType' object has no attribute 'canvas'

Is there a way to get "proper" artists for ArtistAnimation class?

[gokceneraslan]

Here is how the result of plot1() looks like:

[has2k1]

I have not tried to do animations, may be this issue can help straighten that out.

The problem with the plot2 function is that, ggplot.draw() returns a figure. That means you get 50 figures, since plotnine creates the figures. When you have a figure you can obtain the artists with figure.get_children(), but I think that is a catch-all for every artist not just those for the data. And, I think you cannot easily move artists from one figure to another.

So, I do not think ArtistAnimation can be used. Need to think of a nice way of going about this.