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"""
hexbin is an axes method or pyplot function that is essentially a
pcolor of a 2-D histogram with hexagonal cells.
"""
import numpy as np
import matplotlib.pyplot as plt
import matplotlib.mlab as mlab
delta = 0.025
x = y = np.arange(-3.0, 3.0, delta)
X, Y = np.meshgrid(x, y)
Z1 = mlab.bivariate_normal(X, Y, 1.0, 1.0, 0.0, 0.0)
Z2 = mlab.bivariate_normal(X, Y, 1.5, 0.5, 1, 1)
Z = Z2-Z1 # difference of Gaussians
x = X.ravel()
y = Y.ravel()
z = Z.ravel()
if 1:
# make some points 20 times more common than others, but same mean
xcond = (-1 < x) & (x < 1)
ycond = (-2 < y) & (y < 0)
cond = xcond & ycond
xnew = x[cond]
ynew = y[cond]
znew = z[cond]
for i in range(20):
x = np.hstack((x,xnew))
y = np.hstack((y,ynew))
z = np.hstack((z,znew))
xmin = x.min()
xmax = x.max()
ymin = y.min()
ymax = y.max()
gridsize=30
plt.subplot(211)
plt.hexbin(x,y, C=z, gridsize=gridsize, marginals=True)
plt.axis([xmin, xmax, ymin, ymax])
cb = plt.colorbar()
cb.set_label('mean value')
plt.subplot(212)
plt.hexbin(x,y, gridsize=gridsize)
plt.axis([xmin, xmax, ymin, ymax])
cb = plt.colorbar()
cb.set_label('N observations')
plt.show()
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