[R] determining the order in which points are plotted

Greg Snow Greg.Snow at imail.org
Tue Jan 25 18:53:06 CET 2011

With large numbers of points you might want to consider hexagonal binning instead of scatter plots.  I don't know of any tools that both do the binning and take groups into account, but you could think it through and work something out.

Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Mike Miller
> Sent: Monday, January 24, 2011 5:39 PM
> To: David Winsemius
> Cc: R-Help List
> Subject: Re: [R] determining the order in which points are plotted
> On Mon, 24 Jan 2011, David Winsemius wrote:
> > On Jan 24, 2011, at 6:49 PM, Mike Miller wrote:
> >
> >> I make plenty of scatterplots, especially using scatterplot.matrix
> from
> >> library(car).  One thing I don't know how to do is determine which
> >> points are plotted last.  Sometimes I plot a large number of points
> for
> >> multiple groups represented by different colors.
> >
> > ?points
> Thanks for the tip.  I guess I would make vectors for x, y and col in
> the
> desired order and the first elements would be plotted first:
>     Graphical parameters ‘pch’, ‘col’, ‘bg’, ‘cex’ and ‘lwd’ can be
>     vectors (which will be recycled as needed) giving a value for each
>     point plotted.  If lines are to be plotted (e.g. for ‘type = "b"’/
>     the first element of ‘lwd’ is used.
> Suppose I'm plotting 10,000 points in a 10 x 10 scatterplot matrix
> (roughly what I'm actually doing).  That's a total of 1 million points.
> It might take a while, but I can wait.  However, I'm not sure how to
> get
> the coordinates right for additional points in a scatterplot matrix.
> Maybe I need to study that source code.
> I did figure out recently how to use transparent points to get the axes
> right.  Color "#ffffff00" does that trick for me -- that's white color
> with zero opaqueness, full transparency.
> Mike
> --
> Michael B. Miller, Ph.D.
> Minnesota Center for Twin and Family Research
> Department of Psychology
> University of Minnesota

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