[Matplotlib-users] double tick labels (bottom and top, but with different labels)

[vincent.adrien at gmail.com]

Hi Pierre,

I am not sure that label2 can be used for what you want to do. See for
example: https://github.com/matplotlib/matplotlib/issues/8181 . If it
can, I would be eager to know too :)! But I have currently little hopes
that there is an easy *dedicated* method available right now, as Jody K.
recently opened an issue on the GitHub tracker, about a very similar
problem: https://github.com/matplotlib/matplotlib/issues/10976

At least, as  a workaround, a twinned axis allows to get things
reasonably working without too much hassle (I think). Here is an example
that uses uses `FuncFormatter` and seems to be OK, even when
interactively playing with it.
```python
import matplotlib.pyplot as plt
from matplotlib.ticker import FuncFormatter, MultipleLocator

fig, ax = plt.subplots(num="example_pierre", clear=True)

# A dummy plot
xx, yy = [10, 20, 30], [1, 4, 9]
ax.plot(xx, yy)
ax.set_ylabel("An y-label")
ax.set_xlabel("Quantity $x$")
ax.xaxis.set_major_locator(MultipleLocator(10))

# Secondary labelling with twiny
k = 5
ax1 = ax.twiny()
ax1.plot(xx, yy, ls="", color="none")  # dummy trace
ax1.xaxis.set_major_locator(ax.xaxis.get_major_locator())
ax1.xaxis.set_major_formatter(FuncFormatter(lambda x, pos: f"{k*x:g}"))
ax1.set_xlabel(f"{k} times quantity $x$")

fig.show()
fig.savefig(fig.get_label() + ".pdf")
```

Hopefully this helps a bit.

Best
Adrien

PS: If there are better solution to share the ticker and the view
limits, I am interesting to know about it :).


Le 25/04/2018 à 05:34, Pierre Haessig a écrit :
> Hello,
> 
> 
> I'd like to know if it's possible to get a sort of double tick labeling
> (e.g. bottom and top), but with different labels. One way to think of my
> use case is that there are two different units for the x data (or more
> precisely in my case, I've two different x quantities which are bound by
> a linear relationship).
> 
> The result I'd like is the right part of the attached image (it's a
> Gimp-edited mockup composition of the two actual plots on the left).
> 
> I've tried to play with the double labeling of a single axe. Indeed, the
> following two calls put the double labeling
> 
>     ax1.xaxis.set_ticks_position('both')
>     ax1.xaxis.set_tick_params(labeltop=True)
> 
> However, when I want to alter only the top labels using
> 
>     for tick, l in zip(ax1.xaxis.get_major_ticks(), l2):
>         tick.set_label2(l)
> 
> I get no visible change on the plot. (full script attached). Did I need
> to call some update ?
> 
> Did I miss something with the proper way to call Tick.set_label2?
> 
> Looking at the source code of ax1.xaxis.set_ticklabels, there is
> something I don't get. First it sets a FixedFormatter(ticklabels), and
> then it sets label1 and/or label2 for each Tick object. So in the end,
> where is the text coming from?
> 
> 
> Also, to complement the second series of tick labels, I'd like a second
> axis label as well. However, I only know
> ax.xaxis.set_label_position('top') to move xlabel to the top, not to get
> a 2nd one...
> 
> 
> As an alternative approach, I see twinx. I didn't try it yet, because I
> feel like my objective is not of the objective of twinx (e.g. I'm
> plotting only a single dataset, not two). However, I suspect it's
> possible to 'bend" twinx to get what I want. What do you think.
> 
> 
> Thank you in advance for your ideas.
> 
> 
> Best,
> 
> Pierre
> 
> 
> 
> 
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