Question

I have a matplotlib figure that I want to be able to switch between 2D and 3D projections. I can go from 2D to 3D but I can’t seem to work out how to go the other way. Example…

import numpy as np
from mpl_toolkits.mplot3d import Axes3D
import matplotlib.pyplot as plt

def randrange(n, vmin, vmax):
    return (vmax-vmin)*np.random.rand(n) + vmin

fig = plt.figure()

# Create a 3D scatter plot...
ax = fig.add_subplot(111, projection='3d')
n = 100
for c, m, zl, zh in [('r', 'o', -50, -25), ('b', '^', -30, -5)]:
    xs = randrange(n, 23, 32)
    ys = randrange(n, 0, 100)
    zs = randrange(n, zl, zh)
    ax.scatter(xs, ys, zs, c=c, marker=m)

ax.set_xlabel('X Label')
ax.set_ylabel('Y Label')
ax.set_zlabel('Z Label')

# Now I want a 2D plot...
ax.cla()
ax = fig.add_subplot(111)
ax.plot(xs, ys)

plt.show()

The plot stays in the 3D projection and projection="2D" isn’t a valid kwarg…

I thought perhaps ax.clf() would do what I wanted and let me define a new figure. But it just gives me the following error:
ValueError: Unknown element o

Can anyone give me a hint as to the solution to this? Is the ValueError related to the problem or a hint to something else wrong with my setup? Is there a kwarg to switch the projection from 3D to 2D?

Answer 1

I believe I have found one possible solution, although it seems to result in a bit of a memory issue. I suspect that it isn’t actually deleting the initial plot data, just removing it from the figure so memory usage does climb every time the projection is changed.

# Delete the 3D subplot
self.fig.delaxes(self.axes)
# Create a new subplot that is 2D
self.axes = self.fig.add_subplot(111)
# 2D scatter
self.axes.plot(10*np.random.randn(100), 10*np.random.randn(100), 'o')
# Update the figure
self.canvas.draw()