setting color range in matplotlib patchcollection

Question

I am plotting a PatchCollection in matplotlib with coords and patch color values read in from a file.

The problem is that matplotlib seems to automatically scale the co

Answer 1

Use p.set_clim([5, 50]) to set the color scaling minimums and maximums in the case of your example. Anything in matplotlib that has a colormap has the get_clim and set_clim methods.

As a full example:

import matplotlib
import matplotlib.pyplot as plt
from matplotlib.collections import PatchCollection
from matplotlib.patches import Circle
import numpy as np

# (modified from one of the matplotlib gallery examples)
resolution = 50 # the number of vertices
N = 100
x       = np.random.random(N)
y       = np.random.random(N)
radii   = 0.1*np.random.random(N)
patches = []
for x1,y1,r in zip(x, y, radii):
    circle = Circle((x1,y1), r)
    patches.append(circle)

fig = plt.figure()
ax = fig.add_subplot(111)

colors = 100*np.random.random(N)
p = PatchCollection(patches, cmap=matplotlib.cm.jet, alpha=0.4)
p.set_array(colors)
ax.add_collection(p)
plt.colorbar(p)

plt.show()

Now, if we just add p.set_clim([5, 50]) (where p is the patch collection) somewhere before we call plt.show(...), we get this: