Re: [Matplotlib-users] Controlling zorder of individual elements of the same type...

[Fernando P. <Fer...@co...>]

John Hunter wrote:
> Hmm, seems to work for me -- you didn't specify the colors in your
> example which makes it hard to test, so I'll add them

Weird.  I ran this a ton of times, and in _most_ cases I get your same 
results.  And yet a _few_ times, and only when I pasted the code in an 
interactive window, the horizontal line ends below the sine/cosine plots. 
Very, very strange.

> Well the zorder kwarg is your friend -- did you see
> examples/zorder_demo.py ?  Eg
> 
>   plot(x,y, zorder=100)  # I'm on top!

I did read it, but I guess I misunderstood the docstring on top.  I understood 
it as meaning that you could only reorder classes of objects relative to one 
another (lines, text, patches), but not individual lines within the class of 
all lines.

> Now, if I recall correctly, python sort doesn't guarantee preserving
> order for equal element.  Since the order in the respective list
> (patches, lines, etc) *is* determined by the order of the plot
> commands, we might be better off with 
> 
>         dsu = [ (a.zorder, i, a) for i, a in enumerate(artists)]
>         dsu.sort()
>         
>         for zorder, i, a in dsu:
>             a.draw(renderer)
> 
> to guarantee relative order for artists with the same zorder.
> 
> Or is sort relative order preserving for equal elements?

Well, the funny thing about my sometimes-odd results, is that in python 2.3, 
list.sort _is_ stable:

http://py-stablesort.sourceforge.net/doc/2002_07_28_pythonowns_archive.html
http://mail.python.org/pipermail/python-list/2003-April/160326.html

So I'm not quite sure why I get odd results in a few cases.  And I can't seem 
to find a reliable way to repeat the behavior.

But thanks for the clarification on the zorder argument, that's enough for me 
to get the behavior I need.

I'll update the zorder_demo example with a more explicit docstring so others 
don't fall into the same confusion.

Cheers,

f