[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
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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