[R] Plot symbols for more than 25 groups

Prof Brian Ripley ripley at stats.ox.ac.uk
Fri Apr 2 16:52:18 CEST 2004

On Fri, 2 Apr 2004, John Fox wrote:

> I may misunderstand your question, so perhaps this answer isn't what you're
> looking for: 
> A short time ago, Henrik Bengtsson posted a function to r-help (search for
> plotSymbols in the list archive) that displays all available symbols. I
> think that it's fair to say that fewer than 25 of these could be
> characterized as distinct geometric symbols. 

example(points) shows you there are 18, unless you count shadings.

> On the other hand, the colour space for R is very large; see, e.g.,
> help("colours") and the help pages linked to it. 
> Moreover, if you take combinations of filled symbols and even basic colours,
> you could in principle represent more than 25 groups. I wonder, however,
> whether someone viewing a graph with so many different symbols will be able
> to parse the information.

They may, but long before 18 I would use more recognizable symbols, for
example l/case letters (and u/case too if required), or even numbers.  I
was yesterday looking at a thesis which plotted 40 odd different items on
various multivariate displays, and the need was mainly to identify the
apparent misfits.

You would do well to get people to recognize more than a dozen spot
colours, too -- we are tuned to recognizing quite large blobs of colour.
We see only about a dozen colours in a rainbow, which has infinitely many 
and they are adjacent.

Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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