creating a multi colored graph with respect to the values in y-axis

[Ravikanth]

On Jun 15, 11:57 am, Wanderer <wande... at dialup4less.com> wrote:
> On Jun 15, 12:00 pm, Ravikanth <vvnrk.vanapa... at gmail.com> wrote:
>
>
>
>
>
> > On Jun 15, 10:32 am, Wanderer <wande... at dialup4less.com> wrote:
>
> > > On Jun 15, 11:04 am, Ravikanth <vvnrk.vanapa... at gmail.com> wrote:
>
> > > > Hi all,
>
> > > > I am a beginner in python. I need to implement a graph with multiple
> > > > colors in it.
> > > > In a way, I have a function which varies with respect to time and
> > > > amplitude. I have time on x-axis and amplitude on y-axis. Lets say the
> > > > amplitude of the graph is divided into 4 ranges, say 1-3,3-5,5-9,
> > > > 10-3. I need to plot the graph in such a way that, when the values of
> > > > amplitude are in a particular range say 1-3, the color of graph should
> > > > be red.
> > > > If the amplitude is in the range from 3-5 the graph need to be in
> > > > color blue etc..,
>
> > > > Can somebody guide me on this, how to achive this functionality.
>
> > > > Regards,
> > > > Ravikanth
>
> > > Check out the examples in matplotlib.
>
> > >http://matplotlib.sourceforge.net/examples/pylab_examples/multicolore...quoted text -
>
> > > - Show quoted text -
>
> > I did go through the side wanderer.
>
> > I wasn't able to figure out the usage of boundaryNorm and
> > lc.set_array(z) , in that link.
> > according to my understanding,
>
> > cmap = ListedColormap(['r', 'g', 'b'])
> > norm = BoundaryNorm([-1, -0.5, 0.5, 1], cmap.N)
>
> > In the above lines of code, as per my understanding,
> > Listedcolor map, maps the colors r,g and b to specific indexes into
> > cmap
> > i.e cmap(0) represents red,
> > cmap(1) represents blue
> > cmap(2) represents green.
> > for any index greater than 3 a color of blue is returned..
>
> > >>> cmap = ListedColormap(['r', 'g', 'b'])
> > >>> cmap(0)
>
> > (1.0, 0.0, 0.0, 1.0)>>> cmap(1)
>
> > (0.0, 0.5, 0.0, 1.0)>>> cmap(2)
>
> > (0.0, 0.0, 1.0, 1.0)>>> cmap(3)
>
> > (0.0, 0.0, 1.0, 1.0)
>
> > In this context, I was not able to understand what does boundaryNorm
> > does.
> > We have 3 colors and we are using 4 values as argument in boundaryNorm.
> > [-1, -0.5, 0.5, 1], the comment reads slope of 'z' is being mapped to
> > the values in boundary norm. How is it handled.
> > Does the function call " lc.set_array(z) " does it ?  what is the
> > exact use of linecollection.set_array(z) in this context.
>
> > Thanks,
> > Ravikanth
>
> The colors are referring to the slope of the line. Change
> 'lc.set_array(z)' to 'lc.set_array(y)' and it might be easier to
> understand.  Here are the steps.
>
> 1. Define the functions x,y and z,
> 2. Define the colors 'red', 'green' and 'blue' with ListedColorMap
> 3. Define the three regions, (-1.0 to -0.50, -0.50 to 0.50, 0.50 to
> 1.0) with BoundaryNorm([-1,-0.50, 0.50,1], cmap.N).
>    (Why they add the trailing zero in 0.50 and don't change 1 to 1.0;
> I don't know)
> 4. Create an array of (x,y) points.
> 5. Create a collection of tiny segments [(x1,y1),(x2,y2)] and color
> them with cmap using the boundary rules of norm. lc =
> LineCollection(segments, cmap=cmap, norm=norm)
> 6. Use lc.set_array(y) to determine how to color the segments.
> 7. Plot it.- Hide quoted text -
>
> - Show quoted text -

Hi Wanderer,

Thanks for your help. It works now.
Just wanted to know how to go about when I have to do my color mapping
not only with respect to range of values on y-axis but also based on
some other conditions as well. i.e, say ( range && <condtion1> &&
<condition2> ) where condition1 could be occurance of some event say,
a flag1 is set true and condition2 may be another flag2 set to false.
Just wanted to use my color mapping not only based on boundaries but
also on occurance of other events as well.
In this context do i have to modify the source of BoundaryNorm in
matplotlib function...?? Can you give me some insights into this.

Regards,
Ravikanth