For this to work correctly, you need to manually keep two axes in sync
(you can use a callback). Also note that this approach cannot be used
with aspect=1 & adjustable=bbox.
Another way is to use axes_grid1 toolkit.
Here is the modified version of your script w/ axes_grid1.
Regards,
-JJ
import numpy as np
import matplotlib
import matplotlib.colorbar as cb
import matplotlib.pyplot as plt
y = np.reshape(np.arange(0, 1000000, 1), (20000, 50))
test = 'hot'
f1 = plt.figure(1)
f1.patch.set_facecolor('#c0c0c0')
import mpl_toolkits.axes_grid1 as axes_grid1
# use axes_grid1.host_axes
ax1 = axes_grid1.host_axes([0.09, 0.15, 0.82, 0.80])
axc = f1.add_axes([0.09, 0.05, 0.82, 0.05])
im1 = ax1.imshow(y, cmap=test, aspect='auto', origin='lower')
cb.Colorbar(axc, im1, orientation='horizontal')
# use twin() not twinx()
ax2 = ax1.twin()
# make ticklabels on the top invisible
ax2.axis["top"].toggle(ticklabels=False)
fmtr = matplotlib.ticker.FuncFormatter(lambda x,pos: "%.2f"% (x*2,))
ax2.yaxis.set_major_formatter(fmtr)
plt.show()
On Sat, Mar 12, 2011 at 9:01 AM, Thomas Brezinski
<thom...@arlut.utexas.edu> wrote:
> Jason Stone, on 2011-02-18 14:39, wrote:
>> Good afternoon all,
>> One last matplotlib question for the group for today. On one of my GUI
>> plots, I'm calling imshow on an array of data (to display it in the same
>> way
>> MATLAB's imagesc command does). I'd like to add a second y-axis to the
>> right side of the plot that is completely dependent on the values on the
>> primary y-axis. Essentially, for each y-axis tick point, I'll put the
>> y-axis 'value' into a formula and then put the result on the second
>> y-axis.
>> I did this in MATLAB by essentially overlaying a second set of axes over
>> the plot, but I haven't found the exact way to do it with matplotlib yet.
>> I've seen a few examples online, but they all use the second overlaid
>> plot
>> to actually plot new data - I wouldn't be doing this.
>> Would I need to use the twinx (or twiny) function?
>> Are there examples of this on the web that I haven't found that somebody
>> could point me towards?
>
> Hi Jason,
>
> here's an example that does what you want, using e^x as the
> formula, change the paramter to fmtr to suit your needs:
>
> ax = plt.subplot(1,1,1)
> ax.plot(np.sin(np.linspace(0,np.pi)))
> ax2 = ax.twinx()
> ax2._sharey = ax # share both x and y
> fmtr = mpl.ticker.FuncFormatter(lambda x,pos: "%.2f"%np.exp(x))
> ax2.yaxis.set_major_formatter(fmtr)
> plt.draw()
>
> best,
> --
> Paul Ivanov
> 314 address only used for lists, off-list direct email at:
> http://pirsquared.org | GPG/PGP key id: 0x0F3E28F7
>
>
> Paul,
> I am currently doing something very similar and was hoping I could ask for a
> little clarification. I want to have two y axes where the ticks are in the
> same locations and the 2nd y-axis labels are just twice the 1st y-axis
> labels. When I implement your example, I don't quite understand how to
> ensure the ticks are at the same locations. Also, when the data changes to a
> new image, the 1st y-axis updates but the 2nd y-axis does not. Is there a
> convenient way to force both to update each time, or does the figure need to
> be cleared and essentially built from scratch each time.
>
> for example, with the following code:
>
> import numpy as np
> import matplotlib
> import matplotlib.colorbar as cb
> import matplotlib.pyplot as plt
>
> y = np.reshape(np.arange(0, 1000000, 1), (20000, 50))
> test = 'hot'
> f1 = plt.figure(1)
> f1.patch.set_facecolor('#c0c0c0')
> ax1 = f1.add_axes([0.09, 0.15, 0.82, 0.80])
> axc = f1.add_axes([0.09, 0.05, 0.82, 0.05])
> im1 = ax1.imshow(y, cmap=test, aspect='auto', origin='lower')
> cb.Colorbar(axc, im1, orientation='horizontal')
> ax2 = ax1.twinx()
> ax2._sharey = ax1 # share both x and y
> fmtr = matplotlib.ticker.FuncFormatter(lambda x,pos: "%.2f"%np.exp(x))
> ax2.yaxis.set_major_formatter(fmtr)
> plt.show()
>
> The ticks on the right are obviously at different locations compared to the
> left ticks. Also, if imshow was to be called a new array of data, the ticks
> on the right would remain the same. So is there an easy way to force the
> locations to be the same, and is there an easy way force the right y-axis to
> update each time? Thank you very much for your time and help.
>
> -Thomas
>
>
>
>
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