Plotting, hold-on, colors

[Matthias Brennwald]

On Mon, 2008-09-01 at 21:00 -0500, help-octave-request at octave.org wrote:
> Message: 6
> Date: Mon, 01 Sep 2008 18:39:12 -0400
> From: Ben Abbott <bpabbott at mac.com>
> Subject: Re: Plotting, hold-on, colors
> To: Ben Boxman <bboxman at walla.com>
> Cc: help-octave at octave.org
> Message-ID: <FE85B1CB-788E-40F2-A0BF-873BE2EF2482 at mac.com>
> Content-Type: text/plain; charset="us-ascii"
> 
> 
> On Sep 1, 2008, at 5:25 PM, Ben Boxman wrote:
> 
> >
> > Hi,
> >
> >  I've compiled the latest Octave (3.0.2) And the latest released  
> > gnuplot
> > (4.2.3).
> >
> >  I'm vexed by octave/gnuplot not changing colors when plotting  
> > additional
> > plots with hold-on. Yes, I know I can set colors manually (or pass
> all
> > arguments to one big plot call) -- but this is:
> > 1) Cumbersome for normal plots.
> > 2) Even more cumbersome when using hist() and other built-in
> functions
> > on-top of plot (with hist, you can get the output, and then call
> yet  
> > another
> > function (bar -- that doesn't produce exactly the same results  
> > ([x,y] =
> > hist(z); bar(y,x);  -- is visually different than hist(z) --  
> > probably some
> > style default?)....).
> >
> >  This used to work properly in previous (<2.9.x) versions of
> octave.  
> > I use
> > plots extensively, typically, I'll crunch some numbers in the  
> > command line
> > and blurt them out as a plot/histogram (much easier to do this in  
> > octave
> > than in gnuplot, any manipulation/processing/filtering is so much  
> > easier
> > inside of octave). Just about every second plot I make involves  
> > multiple
> >
> >  Is there any quick solution for this?
> >
> >  Is this a gnuplot issue (e.g. like the zoom problem)? Will this
> be  
> > solved
> > if I compile the unstable gnuplot 4.3?
> >  Is there any way I can patch octave to fix this (e.g., changing the
> > default 'blue' to something cyclic, and intercepting hold and  
> > resetting said
> > cyclic variable?)?
> >
> >
> > Man thanks,
> >
> > Ben Boxman
> 
> The Octave developers are actively working to improve Octave's  
> compatibility with Matlab.
> 
> Regarding  the order of the colors, you can change the order by  
> modifying the "colororder" property associated with the axis.  See ...
> 
>  > get (gca, 'colororder')
> 
>   ans = 0.00000 0.00000 1.00000
>         0.00000 0.50000 0.00000
>         1.00000 0.00000 0.00000
>         0.00000 0.75000 0.75000
>         0.75000 0.00000 0.75000
>         0.75000 0.75000 0.00000
>         0.25000 0.25000 0.25000
> 
> so you could
> 
>         colors = get (gca, 'colororder')
> 
> them modify the colors and/or order and then
> 
>         set (gca, 'colororder', colors)
> 
> Is that sufficient for you needs?
> 
> Ben

As far as I can tell, the above solution works with plots where all
lines (=data sets) are plotted using one single plot command.

However, the original question was related to the situation, where one
plots the first data set using plot(...), then 'hold on', and the plot
another data set above the first using a second plot(...). I believe to
remember that Matlab does indeed use a different color for the second
plot (but it's a long time since I used Matlab), so I'd suggest to
change this behaviour in some future version of Octave. In the meantime,
I'd suggest to write a custom function that handles the plot color and
the 'hold on', e.g. somthing like this (not tested):


function h = my_plot (x,y)

global my_col

if ~exist('my_col')
	my_col = 0;
end
my_col = my_col+1;
c = get (gca,'colororder); c = c(my_col,:);
plot (x,y,c)

endfunction