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

[Chad K. <cck...@gm...>]

On Dec 8, 2008, at 2:00 PM, Ryan May wrote:

> 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

Thanks all.  I had tried something close, but it didn't work.  This  
works great.