Thread: [Matplotlib-users] question about setting colors of lines using colormap

Hi all,

i would like to set the colors of the lines i plot (using the plot function)
to go from red to blue, in evenly spaced interval. that is, imagine a color
map from red to green, where i plot n-many lines, each receiving a color
from this color map, starting at the red end and going to green.

the docs say how to set the color cycle of lines set by plot, using:

matplotlib.axes.set_default_color_cycle(['r', 'y', 'g', 'b'])

but this only allows me to use named colors, and here i am looking to use
shades from red to green.
my question is: first, how can i generate N evenly spaced colors from the
red spectrum to the green spectrum? and two, how can i make it so plot uses
these colors for its line plots?

thanks very much.

Not too long ago, I posted an example of this to the list. The code  
near the bottom of that thread is a little more general than the one  
at the top and shows, three different ways to cycle through the colors  
of a colormap.

Hope that helps,
-Tony


On Jul 14, 2009, at 9:51 AM, per freem wrote:

> Hi all,
>
> i would like to set the colors of the lines i plot (using the plot  
> function) to go from red to blue, in evenly spaced interval. that  
> is, imagine a color map from red to green, where i plot n-many  
> lines, each receiving a color from this color map, starting at the  
> red end and going to green.
>
> the docs say how to set the color cycle of lines set by plot, using:
>
> matplotlib.axes.set_default_color_cycle(['r', 'y', 'g', 'b'])
>
> but this only allows me to use named colors, and here i am looking  
> to use shades from red to green.
> my question is: first, how can i generate N evenly spaced colors  
> from the red spectrum to the green spectrum? and two, how can i make  
> it so plot uses these colors for its line plots?
>
> thanks very much.
> ------------------------------------------------------------------------------
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Hi Tony,

thanks for the pointer.  that code does not run for me, it generates the
following error:

ttributeError                            Traceback (most recent call last)

color_cycle.py in <module>()
     63 if __name__ == '__main__':
     64     n_lines = 10
---> 65     cycle_cmap(length=n_lines)
     66     x = np.linspace(0, 10)
     67     for shift in np.linspace(0, np.pi, n_lines):

color_cycle.py in cycle_cmap(cmap, length)
     59     idx = np.linspace(crange['start'], crange['stop'],
length).astype(np.int)
     60     colors = cm(idx)
---> 61     mpl.axes.set_default_color_cycle(colors.tolist())
     62
     63 if __name__ == '__main__':

/Library/Python/2.5/site-packages/matplotlib/axes.pyc in
set_default_color_cycle(clist)
    113     """
    114     _process_plot_var_args.defaultColors = clist[:]
--> 115     rcParams['lines.color'] = clist[0]
    116
    117 class _process_plot_var_args:

/Library/Python/2.5/site-packages/matplotlib/__init__.pyc in
__setitem__(self, key, val)
    603 instead.'% (key, alt))
    604                 key = alt
--> 605             cval = self.validate[key](val)
    606             dict.__setitem__(self, key, cval)
    607         except KeyError:

/Library/Python/2.5/site-packages/matplotlib/rcsetup.pyc in
validate_color(s)
    160 def validate_color(s):
    161     'return a valid color arg'
--> 162     if s.lower() == 'none':
    163         return 'None'
    164     if is_color_like(s):

AttributeError: 'list' object has no attribute 'lower'
WARNING: Failure executing file: <color_cycle.py>

any idea what might be wrong?


On Tue, Jul 14, 2009 at 10:14 AM, Tony S Yu <to...@mi...> wrote:

> Not too long ago, I posted an example of this to the list<http://www.nabble.com/Where-to-post-examples-%2528specifically%252C-one-that-may-be-useful-for-time-evolution-plots%2529-td23901837.html>.
> The code near the bottom of that thread is a little more general than the
> one at the top and shows, three different ways to cycle through the colors
> of a colormap.
>
> Hope that helps,
> -Tony
>
>
> On Jul 14, 2009, at 9:51 AM, per freem wrote:
>
> Hi all,
>
> i would like to set the colors of the lines i plot (using the plot
> function) to go from red to blue, in evenly spaced interval. that is,
> imagine a color map from red to green, where i plot n-many lines, each
> receiving a color from this color map, starting at the red end and going to
> green.
>
> the docs say how to set the color cycle of lines set by plot, using:
>
> matplotlib.axes.set_default_color_cycle(['r', 'y', 'g', 'b'])
>
> but this only allows me to use named colors, and here i am looking to use
> shades from red to green.
> my question is: first, how can i generate N evenly spaced colors from the
> red spectrum to the green spectrum? and two, how can i make it so plot uses
> these colors for its line plots?
>
> thanks very much.
>
> ------------------------------------------------------------------------------
> Enter the BlackBerry Developer Challenge
> This is your chance to win up to $100,000 in prizes! For a limited time,
> vendors submitting new applications to BlackBerry App World(TM) will have
> the opportunity to enter the BlackBerry Developer Challenge. See full prize
>
> details at:
> http://p.sf.net/sfu/Challenge_______________________________________________
> Matplotlib-users mailing list
> Mat...@li...
> https://lists.sourceforge.net/lists/listinfo/matplotlib-users
>
>
>

On Jul 14, 2009, at 3:12 PM, per freem wrote:

> Hi Tony,
>
> thanks for the pointer.  that code does not run for me, it generates  
> the following error:
>
> ttributeError                            Traceback (most recent call  
> last)
>
....
>
> /Library/Python/2.5/site-packages/matplotlib/rcsetup.pyc in  
> validate_color(s)
>     160 def validate_color(s):
>     161     'return a valid color arg'
> --> 162     if s.lower() == 'none':
>     163         return 'None'
>     164     if is_color_like(s):
>
> AttributeError: 'list' object has no attribute 'lower'
> WARNING: Failure executing file: <color_cycle.py>
>
> any idea what might be wrong?

Hmm, it looks like there was a fix added a couple of months ago (svn  
revision 7164). If you're on trunk, then updating it should fix this  
problem. If you're not on trunk: I don't think any official releases  
have occurred since this fix, so I don't think updating to the last  
official release will help.

In any case, I think this error only affects the ``cycle_cmap``  
function in the code (calls to ``cmap_intervals`` should work fine).  
If you comment out the 4 lines of code after the comment "Change the  
default color cycle", I believe everything should work fine.

-Tony

I also recently posted an example that may do something similar to what you
are after, you can have a look here:
http://www.nabble.com/contribute-to-gallery--Or%2C-just-advice-on-changing-colors-automagically....-td24419101.html#a24427781



per freem-2 wrote:
> 
> Hi all,
> 
> i would like to set the colors of the lines i plot (using the plot
> function)
> to go from red to blue, in evenly spaced interval. that is, imagine a
> color
> map from red to green, where i plot n-many lines, each receiving a color
> from this color map, starting at the red end and going to green.
> 
> the docs say how to set the color cycle of lines set by plot, using:
> 
> matplotlib.axes.set_default_color_cycle(['r', 'y', 'g', 'b'])
> 
> but this only allows me to use named colors, and here i am looking to use
> shades from red to green.
> my question is: first, how can i generate N evenly spaced colors from the
> red spectrum to the green spectrum? and two, how can i make it so plot
> uses
> these colors for its line plots?
> 
> thanks very much.
> 
> ------------------------------------------------------------------------------
> Enter the BlackBerry Developer Challenge  
> This is your chance to win up to $100,000 in prizes! For a limited time, 
> vendors submitting new applications to BlackBerry App World(TM) will have
> the opportunity to enter the BlackBerry Developer Challenge. See full
> prize  
> details at: http://p.sf.net/sfu/Challenge
> _______________________________________________
> Matplotlib-users mailing list
> Mat...@li...
> https://lists.sourceforge.net/lists/listinfo/matplotlib-users
> 
> 

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