Python Matplotlib/Basemap Color Cycling

Question

I'm new to Python and the other programs and I'm attempting to plot 21 members of an ensemble forecast using for loops over the ensemble members, each one having a dedicated number 1-21. When I plot the map, the members all come up blue. I've done some research on colormaps and found that the default maps are not indexed, i.e. I can't call colormap[1] as if it were a list or array. Are there any indexed colormaps out there, or is there any way around this? Simply put, I want to cycle through colors, a different one for each forecast member, using simple numerics.

Answer 1

You could use ax.set_prop_cycle to specify a list of colors to cycle through.

Colormaps are callable, so an easy way to generate colors is to pass an sequence of floats between 0 and 1 to a colormap, which will then return an array of RGBA colors.

For example,

In [93]: jet = plt.cm.jet

In [94]: jet([0,0.5,1])
Out[94]: 
array([[ 0.        ,  0.        ,  0.5       ,  1.        ],
       [ 0.49019608,  1.        ,  0.47754586,  1.        ],
       [ 0.5       ,  0.        ,  0.        ,  1.        ]])

---

import matplotlib.pylab as plt
import matplotlib.rcsetup as rcsetup
import numpy as np

jet = plt.cm.jet
fig, ax = plt.subplots()
N = 20
idx = np.linspace(0, 1, N)
ax.set_prop_cycle(rcsetup.cycler('color', jet(idx)))
x = np.linspace(0, 100, 200)
for i in range(1, N+1):
    ax.plot(x, np.sin(x)+i)
ax.set_ylim(0, N+1)
plt.show()