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Companion notebook to my article about population density and social distancing
import matplotlib
import numpy as np
import matplotlib.pyplot as plt
def cmap_map(function, cmap):
""" Applies function (which should operate on vectors of shape 3: [r, g, b]), on colormap cmap.
This routine will break any discontinuous points in a colormap.
cdict = cmap._segmentdata
step_dict = {}
# Firt get the list of points where the segments start or end
for key in ('red', 'green', 'blue'):
step_dict[key] = list(map(lambda x: x[0], cdict[key]))
step_list = sum(step_dict.values(), [])
step_list = np.array(list(set(step_list)))
# Then compute the LUT, and apply the function to the LUT
reduced_cmap = lambda step : np.array(cmap(step)[0:3])
old_LUT = np.array(list(map(reduced_cmap, step_list)))
new_LUT = np.array(list(map(function, old_LUT)))
# Now try to make a minimal segment definition of the new LUT
cdict = {}
for i, key in enumerate(['red','green','blue']):
this_cdict = {}
for j, step in enumerate(step_list):
if step in step_dict[key]:
this_cdict[step] = new_LUT[j, i]
elif new_LUT[j,i] != old_LUT[j, i]:
this_cdict[step] = new_LUT[j, i]
colorvector = list(map(lambda x: x + (x[1], ), this_cdict.items()))
cdict[key] = colorvector
return matplotlib.colors.LinearSegmentedColormap('colormap',cdict,1024)
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