Re: [Matplotlib-users] a break in the y-axis

[Paul I. <piv...@gm...>]

Paul Ivanov, on 2011-01-22 18:28,  wrote:
> Ilya Shlyakhter, on 2011-01-22 19:06,  wrote:
> > Is it possible to create a "break" in the y-axis so that it has ticks
> > for value 0-.2, then ticks for values .8-1.0, but devotes only a token
> > amount of space to the area 0.2-0.8?
> > I have a dataset with most datapoints in 0-.2 and a couple in .8-1.0,
> > and none in .2-.8 .   The default scaling wastes a lot of space and
> > compresses the data in the 0-.2 range
> > such that it is hard to distinguish.
>  
> Hi Ilya,
> 
> this...
> 
> > p.s. I know I could use two y-axes with different scales; but this
> > would require splitting the data into two different datasets as well,
> > and would not allow connecting all points
> > with one line.
> 
> ... is the way I'd proceed, because it's clean, and requires the
> least amount of work.  Connecting your lines across such breaks
> is misleading - since the magnitude of the slope of the
> connecting line segment arbitrary relative to all other line
> segments. You don't actually have to divide your data, you can
> just replot *all* data on the secondary plot, and then set the x
> and y lims to break up your views on the data. I'm attaching a
> quick sketch of what that would look like. (Note how different
> the outlier line segments would look if we connected them in the
> same manner that all other points are connected).
> 
>   import numpy as np
>   import matplotlib.pylab as plt
>   pts = np.random.rand(30)*.2
>   pts[[7,11]] += .8
>   f,(ax,ax2) = plt.subplots(2,1,sharex=True)
>   
>   ax.plot(pts)
>   ax2.plot(pts)
>   ax.set_ylim(.78,1.)
>   ax2.set_ylim(0,.22)
>   
>   ax.xaxis.tick_top()
>   ax.spines['bottom'].set_visible(False)
>   ax.tick_params(labeltop='off')
>   ax2.xaxis.tick_bottom()
>   ax2.spines['top'].set_visible(False)
> 
> If this is something you really want, though, you can achieve it
> by making your own projection/scale:
> http://matplotlib.sourceforge.net/devel/add_new_projection.html
> 
> Yet another way would be to re-label the tick lines (e.g. make .6
> label be 1.0 and subtract that offset from your two outliers.

forgot the attachment, here it is.

-- 
Paul Ivanov
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