Plotting multiple segments with colors based on some variable with matplotlib

Question

Following the answers of both topics Matplotlib: Plotting numerous disconnected line segments with different colors and matplotlib: how to change data points color based on some variable, I am trying to plot a set of segments given by a list, for instance:

data = [(-118, -118), (34.07, 34.16),
        (-117.99, -118.15), (34.07, 34.16),
        (-118, -117.98), (34.16, 34.07)]

and I would like to plot each segments with a color based on a second list for instance:

color_param = [9, 2, 21]

with a colormap. So far I am using this line to display the segments:

plt.plot(*data)

I was expecting that something like

plt.plot(*data, c=color_param, cmap='hot')

would work but it doesn't. Can anybody help me solving this problem? I would rather work with matplotlib if possible.

Thank you in advance!

Answer 1

You can consider the following:

import numpy as np 
import pylab as pl 

# normalize this
color_param = np.array([9.0, 2.0, 21.0])
color_param = (color_param - color_param.min())/(color_param.max() - color_param.min())

data = [(-118, -118), (34.07, 34.16),
        (-117.99, -118.15), (34.07, 34.16),
        (-118, -117.98), (34.16, 34.07)]

startD = data[::2]
stopD  = data[1::2]



for start, stop, col in zip( startD, stopD,  color_param):
    pl.plot( start, stop, color = pl.cm.jet(col) )

pl.show()

Rememebr that the colormaps pl.cm.hot(0.7) will return a color value when presented a number between 0 and 1. This comes in very handy sometimes, like in your case

Edit:

For a red-to-green colormap:

import pylab as pl 
import matplotlib.colors as col
import numpy as np 

cdict = {'red':   [(0.0,  1.0, 1.0),
                   (1.0,  0.0, 0.0)],
         'green':  [(0.0,  0.0, 0.0),
                   (1.0,  1.0, 1.0)],
         'blue':   [(0.0,  0.0, 0.0),
                    (1.0,  0.0, 0.0)]}

my_cmap = col.LinearSegmentedColormap('my_colormap',cdict,256)


for theta in np.linspace(0, np.pi*2, 30):
    pl.plot([0,np.cos(theta)], [0,np.sin(theta)], color=my_cmap(theta/(2*np.pi)) )

pl.show()