Matplotlib: Colour multiple twinx() axes

Question

I'm currently using matplotlib within Sage to plot some data. I have made it possible to add multiple y axes using this example:

from mpl_toolkits.axes_grid1 import host_subplot
import mpl_toolkits.axisartist as AA
import matplotlib.pyplot as plt

if 1:

    host = host_subplot(111, axes_class=AA.Axes)
    plt.subplots_adjust(right=0.75)

    par1 = host.twinx()
    par2 = host.twinx()

    offset = 60
    new_fixed_axis = par2.get_grid_helper().new_fixed_axis
    par2.axis["right"] = new_fixed_axis(loc="right",
                                        axes=par2,
                                        offset=(offset, 0))

    par2.axis["right"].toggle(all=True)



    host.set_xlim(0, 2)
    host.set_ylim(0, 2)

    host.set_xlabel("Distance")
    host.set_ylabel("Density")
    par1.set_ylabel("Temperature")
    par2.set_ylabel("Velocity")

    p1, = host.plot([0, 1, 2], [0, 1, 2], label="Density")
    p2, = par1.plot([0, 1, 2], [0, 3, 2], label="Temperature")
    p3, = par2.plot([0, 1, 2], [50, 30, 15], label="Velocity")

    par1.set_ylim(0, 4)
    par2.set_ylim(1, 65)

    host.legend()

    host.axis["left"].label.set_color(p1.get_color())
    par1.axis["right"].label.set_color(p2.get_color())
    par2.axis["right"].label.set_color(p3.get_color())

    plt.draw()
    plt.show()

    #plt.savefig("Test")

source: http://matplotlib.org/examples/axes_grid/demo_parasite_axes2.html

However, is it possible to change the colour of the parasite axes? I read somewhere that this method is not very compatible with the original twinx() so that may be complicating things.

Answer 1

Its not necessary to use the AA class, although normally that would save you a few lines of code. I'm not sure what exactly you want to color since the axes consists of many items which can have a color like spines, label, ticklabels etc.

This example shows how to color most of it, its almost identical to the one in the gallery .

import matplotlib.pyplot as plt

fig, host = plt.subplots()
fig.subplots_adjust(right=0.75)

par1 = host.twinx()
par2 = host.twinx()

# move the spine of the second axes outwards
par2.spines["right"].set_position(("axes", 1.2))

p1, = host.plot([0, 1, 2], [0, 1, 2], 'r-', label="Density")
p2, = par1.plot([0, 1, 2], [0, 3, 2], 'g-', label="Temperature")
p3, = par2.plot([0, 1, 2], [50, 30, 15], 'b-', label="Velocity")

host.set_xlim(0, 2)
host.set_ylim(0, 2)
par1.set_ylim(0, 4)
par2.set_ylim(1, 65)

host.set_xlabel("Distance")
host.set_ylabel("Density")
par1.set_ylabel("Temperature")
par2.set_ylabel("Velocity")

lines = [p1, p2, p3]
host.legend(lines, [l.get_label() for l in lines])

for ax in [par1, par2]:
    ax.set_frame_on(True)
    ax.patch.set_visible(False)

    plt.setp(ax.spines.values(), visible=False)
    ax.spines["right"].set_visible(True)

host.yaxis.label.set_color(p1.get_color())
par1.yaxis.label.set_color(p2.get_color())
par2.yaxis.label.set_color(p3.get_color())

par1.spines["right"].set_edgecolor(p2.get_color())
par2.spines["right"].set_edgecolor(p3.get_color())

host.tick_params(axis='y', colors=p1.get_color())
par1.tick_params(axis='y', colors=p2.get_color())
par2.tick_params(axis='y', colors=p3.get_color())

Answer 2

I've figured it out. For some reason using host.twinx() multiple times doesn't work for me- maybe that's a newer feature of matplotlib?

fig, host = plt.subplots()

Ensure that you use fig, host = plt.subplots() and not seperately in two lines. I tried what Rutger Kassies suggested and it worked.

If you write the same thing as:

fig=plt.figure()
host = plt.subplots()

It will not work as the references have changed. In my opinion, fig, host should refer to same reference for this to work.