User list for matplotlib - a matlab compatible plot library for numerical python

Sterling Smith | 15 Nov 2012 18:49

Re: discrete colors from colormap for plt.plot and plt.scatter

Claus,

I think you are looking for something in
http://matplotlib.org/api/colors_api.html

-Sterling

On Nov 15, 2012, at 8:24AM, Claus wrote:

> Hi,
> I have this issue, schematically:
> 
> import numpy as np
> import matplotlib.pyplot as plt 
> 
> x = np.linspace(0.0, a, b)
> 
> for i in range(d):
> 	y1 = f1(x, p1_i, p2_i)
> 	y2 = f2(x, p1_i, p2_i)
> 	plt.scatter(x, y1, c=color[i])
> 	plt.plot(x, y2, '-', c=color[i]
> 
> 
> my question:
> how can I setup color to be d colors from some colormap (like cm.copper or cm.jet), they should be somewhat
"equally" spaced… maybe the loop is not ideal, but I don't know a better way (yet)…
> 
> Thanks for your help,
> Cheers,

(Continue reading)

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Ryan Nelson | 15 Nov 2012 23:41

Re: discrete colors from colormap for plt.plot and plt.scatter

Claus,

I agree with Sterling that the colors api page has a great deal of useful info. However, as another solution to your problem, keep in mind that the predefined colormaps contained in matplotlib.pyplot.cm return color tuples when called with a float between 0 and 1. To illustrate with an extension of your example code, try the following:

import numpy as np
import matplotlib.pyplot as plt
x = np.linspace(0,10,25) # Your x values
# A list of parameters for generating the y values
p = np.linspace(1,10,5)
# An array of values between 0 and 1 with the same length as your parameter list.
d = np.linspace(0, 1, 5)
for i,j in zip(p,d):
    y = np.sin(x*i)
    plt.scatter(x, y, color=plt.cm.copper(j))
    plt.plot(x, y, color=plt.cm.jet(j))
plt.show()

If you have a lot of parameters, hence a large number of plots, you might want to start reading up on collections:
http://matplotlib.org/api/collections_api.html
My understanding is that collections plot faster than many repeated calls to plt.plot or plt.scatter. I've used LineCollection to plot a large number of lines: I don't know which collection to use for repeated scatter plots, though.

Good luck

Ryan

On Thu, Nov 15, 2012 at 12:49 PM, Sterling Smith <smithsp-EMBjEUNh33eBik42HM7KXg@public.gmane.org> wrote:

Claus,

I think you are looking for something in
http://matplotlib.org/api/colors_api.html

-Sterling

On Nov 15, 2012, at 8:24AM, Claus wrote:

> Hi,
> I have this issue, schematically:
>
> import numpy as np
> import matplotlib.pyplot as plt
>
> x = np.linspace(0.0, a, b)
>
> for i in range(d):
> y1 = f1(x, p1_i, p2_i)
> y2 = f2(x, p1_i, p2_i)
> plt.scatter(x, y1, c=color[i])
> plt.plot(x, y2, '-', c=color[i]
>
>
> my question:
> how can I setup color to be d colors from some colormap (like cm.copper or cm.jet), they should be somewhat "equally" spaced… maybe the loop is not ideal, but I don't know a better way (yet)…
>
> Thanks for your help,
> Cheers,
> Claus
>
>
>
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