Re: [Matplotlib-users] discrete non-uniform intervals colorbar

[Eric F. <ef...@ha...>]

James Boyle wrote:
> I wish to make a color filled plot with the colors defined for  
> discrete, non-uniform intervals. Something like:
> 0.0 -0.001  0.001-0.05   0.05-0.2     0.2-0.4      0.4-0.8      0.8-1.0
>     red              blue             green       magenta      
> yellow        cyan
> 
> with the colorbar labeled appropriately.
> I have seen discussions and solutions for discrete colors but not for  
> non-uniform intervals + discrete.
> The last post I saw regarding this type of issue was august 2005 -  
> and a solution was not resolved at that time.
> However, Eric has done a huge amount of work in the intervening time  
> and a smarter person than myself might have a solution now.
> 
> Note that I do not wish just to make contours - although that would  
> be good - but to have a general mapping code that joins allows the  
> color rmapping to be passed to colorbar.
> maybe some sub-class of scalarMappable that could work.

This is very easy for contourf, and is illustrated in the second figure 
made by examples/contourf_demo.py.  For your case above, it would be 
something like

levs = [0, 0.001, 0.05, 0.2, 0.4, 0.8, 1]
colors = ['r', 'b', 'g', 'm', 'y', 'c']
contourf(z, levs, colors=colors)
colorbar()

Unfortunately, although it *should* be just as easy for imshow or 
pcolor, it is not at present; it can be done, probably in several ways, 
but not in such a transparent way.  Attached is a quick attempt at 
something that might be close to what you need.  The right way to do 
this is to make some changes and additions to colors.py and colorbar.py; 
I might get to that in a few days, or, more likely, it might be a few weeks.

Eric

> 
> Thanks for any help.
> 
> --Jim