Multiple y axis using matplotlib not working

Question

I have used following code to plot graph using matplotlib with 4 parameter X=depth, y1=temp, y2=salinity, y3=velocity but value of velocity is not display properly and 2nd and 3rd axes are not adjustable(scale value) as 1st when zoom that has constant scale value, how could i make it adjustable(scale value) ,I mean scale value will be variable for all axes when zoom in zoomout.

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

 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("Depth")
    host.set_ylabel("Temperature")
    par1.set_ylabel("Salinity")
    par2.set_ylabel("Velocity")
    x  = np.array([0,5,10,15,20,25,30,35])
    y1 = np.array([30.340,30.080,29.116,28.395,28.093,28.040,27.975,27.872])
    y2 = np.array([33.130,34.046,35.119,34.933,34.764,34.824,34.860,34.852])
    y3 = np.array([1544.296, 1544.787, 1543.452,1542.280,1541.522,1544.548,1541.523,1541.368])

    p1, = host.plot(x, y1, label="Temperature")
    p2, = par1.plot(x, y2, label="Salinity")
    p3, = par2.plot(x, y3, 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()

If you create "host" using plt.subplot instead of host_subplot, then they should all pan+zoom together as you describe. Do you need to use host_subplot in order to get the nice offset-y-scale that you are using? — DanHickstein
– DanHickstein, Commented Sep 30, 2015 at 14:37
I fixed the indentation issue, so the code should easily run now. — DanHickstein
– DanHickstein, Commented Oct 1, 2015 at 13:50

DanHickstein · Accepted Answer · 2015-10-01 14:15:15Z

1

Here is an example that works that way that you suggest: http://matplotlib.org/examples/pylab_examples/multiple_yaxis_with_spines.html

Basically, they avoid using the "new_fixed_axis" function:

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

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

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

par2.spines["right"].set_position(("axes", 1.2))
par2.spines["right"].set_visible(True)

host.set_xlabel("Depth")
host.set_ylabel("Temperature")
par1.set_ylabel("Salinity")
par2.set_ylabel("Velocity")

x  = np.array([0,5,10,15,20,25,30,35])
y1 = np.array([30.340,30.080,29.116,28.395,28.093,28.040,27.975,27.872])
y2 = np.array([33.130,34.046,35.119,34.933,34.764,34.824,34.860,34.852])
y3 = np.array([1544.296, 1544.787, 1543.452,1542.280,1541.522,1544.548,1541.523,1541.368])

p1, = host.plot(x, y1, 'b', label="Temperature")
p2, = par1.plot(x, y2, 'r', label="Salinity")
p3, = par2.plot(x, y3/10, 'g', label="Velocity/00")

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

tkw = dict(size=4, width=1.5)
host.tick_params(axis='y', colors=p1.get_color(), **tkw)
par1.tick_params(axis='y', colors=p2.get_color(), **tkw)
par2.tick_params(axis='y', colors=p3.get_color(), **tkw)
host.tick_params(axis='x', **tkw)

host.legend()
plt.show()

There is still a little problem with the weird y-axis scales, but at least they zoom+pan together :).

answered Oct 1, 2015 at 14:15

DanHickstein

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1 Comment

sohamkumar Over a year ago

Thanks for the solution and by providing the limit of range of y axis using ylim problem with the weird y-axis scales will be solved.

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