Re: [Matplotlib-users] using color as z-axis for plots

[Ryan M. <rm...@gm...>]

Chad Kidder wrote:
> On Dec 8, 2008, at 12:55 PM, Ryan May wrote:
> 
>> Chad Kidder wrote:
>>> I've got many series of data that I want to plot, and each has an   
>>> additional scalar that is valid for the whole series.  What I want  
>>> to  do is plot all these series on top of each other (plot can do  
>>> this  just fine), but with the additional scalar changing the  
>>> color,  efectively using color as the z-axis.  I'm not seeing how  
>>> to do that.   If there was a function where I could give a color  
>>> map a value and it  would spit out the color, that would work, but  
>>> I haven't seen it.   Thanks for your help.
>> Try using scatter instead of plot.  Specifically, the 'c' keyword  
>> argument:
>>
>>      *c*:
>>        a color. *c* can be a single color format string, or a
>>        sequence of color specifications of length *N*, or a
>>        sequence of *N* numbers to be mapped to colors using the
>>        *cmap* and *norm* specified via kwargs (see below). Note
>>        that *c* should not be a single numeric RGB or RGBA
>>        sequence because that is indistinguishable from an array
>>        of values to be colormapped.  *c* can be a 2-D array in
>>        which the rows are RGB or RGBA, however.

Here's what you're looking for:

import numpy as n
import matplotlib.pyplot as p
import matplotlib.colors as mcolors
import matplotlib.cm as cm

cmap = cm.get_cmap('winter')
norm = mcolors.Normalize(0, 1) #Range of z

nlines = 100
z = n.random.rand(nlines)
x = n.arange(nlines)
t1, t2 = n.meshgrid(x,z)
y = t1+t2-0.5

#Uses normalize to map z values to range of 0 to 1.
#Cmap maps these normalized values to colors
colors = cmap(norm(z))
for ii in range(nlines):
     p.plot(x, y[ii], color=colors[ii])
p.show()

Ryan

-- 
Ryan May
Graduate Research Assistant
School of Meteorology
University of Oklahoma