Question

I’m having a problem trying to plot a series of lines in a 3D plot in MatPlotLib.
When I run the code below all the lines are plotted at the last value of y??? Even though y is correctly incremented in the loop.
Any Help understanding this would be appreciated.
Thanks
David

#========== Code Start=================
import numpy as np
import matplotlib
from matplotlib.figure import Figure
import pylab as plt
from mpl_toolkits.mplot3d import Axes3D


fig = plt.figure()
ax = Axes3D(fig)
x=np.arange(5)
y=np.zeros(len(x))

for i in range(1,10):
    y.fill(i)
    z=plt.randn(len(y))
    ax.plot(xs=x, ys=y, zs=z)#, zdir='z', label='ys=0, zdir=z')
    plt.draw()
    print i,len(y),y,x,z
plt.xlabel('X') 
plt.ylabel('Y')
plt.zlabel('Z')   
plt.show()
#========== Code End=================

Answer 1

It looks like y might be pointed to by all plots. So you are passing the reference to y when you execute ax.plot. It is the same reference each time, but the values are changed on each pass. When the plt.show() is executed the reference to y is used and it is now set at 9. So, create a different object for y on each pass with the values you want for that pass:

y = np.zeros(len(x))
y.file(i)

There might be a numpy command that fills with the value you want in one go, but you get the picture.