Fix a legend in an animation created by celluloid

Question

I want to animate the process of finding the minimum point of a function by different gradient descent optimization methods. For this purpose, I am using matplotlib and celluloid packages. The problem is that it is not possible to fix the legend of the plot in animation and in each loop a new legend is added below the previous legend as you can see in the figure below. is there any way to fix the legend and avoid this problem?

from celluloid import Camera
fig,ax = plt.subplots(1, 1,figsize=(10, 10))
camera = Camera(fig)
for i in range(path1.shape[1])
  ax.contour(x_mesh, y_mesh, z, levels=np.logspace(0, 5, 35), norm=LogNorm(), cmap=plt.cm.jet)
  ax.plot(*minima_, 'r*', markersize=18)

  line, = ax.plot([], [], 'k', label='Simple SGD', lw=2)
  point, = ax.plot([], [], 'ko')
  line.set_data(path1[::,:i])
  point.set_data(path1[::,i-1:i])

  line, = ax.plot([], [], 'r', label='SGD with momentum', lw=2)
  point, = ax.plot([], [], 'ro')
  line.set_data(*path2[::,:i])
  point.set_data(*path2[::,i-1:i])

  line, = ax.plot([], [], 'g', label='SGD with Nesterov', lw=2)
  point, = ax.plot([], [], 'go')
  line.set_data(*path3[::,:i])
  point.set_data(*path3[::,i-1:i])

  line, = ax.plot([], [], 'b', label='SGD with Adagrad', lw=2)
  point, = ax.plot([], [], 'bo')
  line.set_data(*path4[::,:i])
  point.set_data(*path4[::,i-1:i])

  line, = ax.plot([], [], 'c', label='SGD with Adadelta', lw=2)
  point, = ax.plot([], [], 'co')
  line.set_data(*path5[::,:i])
  point.set_data(*path5[::,i-1:i]) 

  line, = ax.plot([], [], 'm', label='SGD with RMSprob', lw=2)
  point, = ax.plot([], [], 'mo')
  line.set_data(*path6[::,:i])
  point.set_data(*path6[::,i-1:i])

  line, = ax.plot([], [], 'y', label='SGD with Adam', lw=2)
  point, = ax.plot([], [], 'yo')
  line.set_data(*path7[::,:i])
  point.set_data(*path7[::,i-1:i])

  line, = ax.plot([], [], 'y', label='SGD with Adamax', lw=2)
  point, = ax.plot([], [], 'y*')
  line.set_data(*path8[::,:i])
  point.set_data(*path8[::,i-1:i])

  line, = ax.plot([], [], 'k', label='SGD with Nadam', lw=2)
  point, = ax.plot([], [], 'kp')
  line.set_data(*path9[::,:i])
  point.set_data(*path9[::,i-1:i])

  line, = ax.plot([], [], 'r', label='SGD with AMSGrad', lw=2)
  point, = ax.plot([], [], 'rD')
  line.set_data(*path10[::,:i])
  point.set_data(*path10[::,i-1:i])

  ax.legend(loc='upper left') 
  camera.snap()
animation = camera.animate()
animation.save('2D_animation_overlap.gif', writer='imagemagick')

So you want an animation instead of just a plot? With the legends fixed during the animation without repetitions as I see here. — SKPS, Jan 24 '20 at 07:02
Yes exactly. Do you have any idea to create such a fixed legend? — hamid mohebzadeh, Jan 24 '20 at 07:36
There is a good example [here](https://stackoverflow.com/questions/44594887/how-to-update-plot-title-with-matplotlib-using-animation). See if this helps. — SKPS, Jan 24 '20 at 07:38
Also, I cannot compile your posted code. Can you post a working code? — SKPS, Jan 24 '20 at 07:48
Sorry, my code is too long and it is not possible to post it here. if you want, I can send it to you by email. However, William's answer solved my problem. — hamid mohebzadeh, Jan 26 '20 at 02:31

William Miller · Accepted Answer · 2020-01-27T04:56:47.173

The best practice here would be to create a custom legend instead of automatically generating a legend, in this case that could be done by

import matplotlib.pyplot as plt
from matplotlib.lines import Line2D

labels = ['Single SGD', 'SGD with momentum', 'SGD with Nesterov', 
          'SGD with Adagrad', 'SGD with Adadelta', 'SGD with RMSprob', 'SGD with Adam', 
          'SGD with Adamax', 'SGD with Nadam', 'SGD with AMSgrad']
colors = ['k', 'r', 'g', 'b', 'c', 'm', 'y', 'y', 'k', 'r']
handles = []
for c, l in zip(colors, labels):
    handles.append(Line2D([0], [0], color = c, label = l))

plt.legend(handles = handles, loc = 'upper left')

which will give you a legend like this:

You don’t need to have any of this in the loop, you can do it before or after and it will still work. It will also work in the loop but redrawing the legend each time is unnecessary.

It would also suffice to simply guard the legend creation with an if statement instead of creating the legend manually. I.e.

    # ...
    if i == 0:
        ax.legend(loc = 'upper left')

But I would recommend against the practice of goading the automatic legend generation in favor of directly creating the legend.

Thank you so much, William. Your second answer was so useful and solved my problem. — hamid mohebzadeh, Jan 26 '20 at 02:29
@hamidmohebzadeh Glad it helped, be sure to mark it as [accepted](https://stackoverflow.com/help/someone-answers) so the question is marked as such for future users — William Miller, Jan 26 '20 at 02:54

Fix a legend in an animation created by celluloid

1 Answers1