I have many lines to plot. Each line has an associated parameter value. I'd like to pick the color for each line based on its parameter value by mapping possible parameter values to the colors in a color map (e.g., gist_rainbow), retrieving colors one at a time (based on the parameter value for a line). If two lines have the same parameter value, I need them to have exactly the same color. Hints? Thanks, Alan Isaac
Oops. I meant to reply to the list.
-Tony
---------- Forwarded message ----------
From: Tony Yu <ts...@gm...>
Date: Sat, Jul 30, 2011 at 10:46 AM
Subject: Re: [Matplotlib-users] parametric line color
To: Alan G Isaac <ala...@gm...>
On Sat, Jul 30, 2011 at 12:03 AM, Alan G Isaac <ala...@gm...> wrote:
> I have many lines to plot.
> Each line has an associated parameter value.
> I'd like to pick the color for each line
> based on its parameter value by mapping
> possible parameter values to the colors
> in a color map (e.g., gist_rainbow),
> retrieving colors one at a time (based
> on the parameter value for a line).
>
> If two lines have the same parameter value,
> I need them to have exactly the same color.
>
> Hints?
>
> Thanks,
> Alan Isaac
>
>
Here's a function to do what you want. (I haven't tested it much so it could
be buggy)
Best,
-Tony
#----
import matplotlib.pyplot as plt
def make_color_manager(parameter_range, cmap='YlOrBr', start=0, stop=255):
"""Return color manager, which returns color based on parameter value.
Parameters
----------
parameter_range : 2-tuple
minimum and maximum value of parameter
cmap : str
name of a matplotlib colormap (see matplotlib.pyplot.cm)
start, stop: int
limit colormap to this range (0 <= start < stop <= 255)
"""
colormap = getattr(plt.cm, cmap)
pmin, pmax = parameter_range
def color_manager(val):
"""Return color based on parameter value `val`."""
assert pmin <= val <= pmax
val_norm = (val - pmin) * float(stop - start) / (pmax - pmin)
idx = int(val_norm) + start
return colormap(idx)
return color_manager
if __name__ == '__main__':
cm = make_color_manager((5, 10), start=100)
plt.plot([0, 1], color=cm(5))
plt.plot([0.5, 0.5], color=cm(7.5))
plt.plot([1, 0], color=cm(10))
plt.legend(('val = 5', 'val = 7.5', 'val = 10'))
plt.show()
On 07/29/2011 06:03 PM, Alan G Isaac wrote: > I have many lines to plot. > Each line has an associated parameter value. > I'd like to pick the color for each line > based on its parameter value by mapping > possible parameter values to the colors > in a color map (e.g., gist_rainbow), > retrieving colors one at a time (based > on the parameter value for a line). > > If two lines have the same parameter value, > I need them to have exactly the same color. > > Hints? Tony's reply may be the right approach for you; but an alternative, if you are plotting a set of lines all at once, is to use a LineCollection, which takes a colors kwarg. (Like all Collections, a LineCollection includes the cm.ScalarMappable mixin.) See http://matplotlib.sourceforge.net/examples/pylab_examples/line_collection2.html but note that the lines within the collection don't have to have the same number of points. Also, Tony's method could be modified easily to use a norm (e.g., an instance of colors.Normalize or of a subclass) in addition to a cmap. Eric > > Thanks, > Alan Isaac > > ------------------------------------------------------------------------------ > Got Input? Slashdot Needs You. > Take our quick survey online. Come on, we don't ask for help often. > Plus, you'll get a chance to win 100ドル to spend on ThinkGeek. > http://p.sf.net/sfu/slashdot-survey > _______________________________________________ > Matplotlib-users mailing list > Mat...@li... > https://lists.sourceforge.net/lists/listinfo/matplotlib-users
On 7/30/2011 12:03 AM, Alan G Isaac wrote: > I'd like to pick the color for each line > based on its parameter value by mapping > possible parameter values to the colors > in a color map (e.g., gist_rainbow), > retrieving colors one at a time (based > on the parameter value for a line). As far as I can tell, the answer is the following. 1. scale the parameter to fall in (0,1) 2. get a color (rgba tuple) as cm.gist_rainbow(scaled_param) 3. plot using that color This works. Cheers, Alan Isaac
On 07/31/2011 04:05 AM, Alan G Isaac wrote: > On 7/30/2011 12:03 AM, Alan G Isaac wrote: >> I'd like to pick the color for each line >> based on its parameter value by mapping >> possible parameter values to the colors >> in a color map (e.g., gist_rainbow), >> retrieving colors one at a time (based >> on the parameter value for a line). > > > > As far as I can tell, the answer is the following. > 1. scale the parameter to fall in (0,1) > 2. get a color (rgba tuple) as cm.gist_rainbow(scaled_param) > 3. plot using that color For completeness: You can call a Colormap instance with either a float in (0,1), or equivalently with an integer in (0, N-1), where N is the number of discrete colors in the lookup table, excluding the over, under, and "bad" colors. The standard colormaps in cm are all created with N=mpl.rcParams['image.lut'], defaulting to 256, but you can make a colormap with any value of N. Eric > > This works. > > Cheers, > Alan Isaac > > > ------------------------------------------------------------------------------ > Got Input? Slashdot Needs You. > Take our quick survey online. Come on, we don't ask for help often. > Plus, you'll get a chance to win 100ドル to spend on ThinkGeek. > http://p.sf.net/sfu/slashdot-survey > _______________________________________________ > Matplotlib-users mailing list > Mat...@li... > https://lists.sourceforge.net/lists/listinfo/matplotlib-users