[R] MacOS X Quartz Rendering? (Solved)

Neil Gunther njgunther at perfdynamics.com
Sat Mar 25 08:11:50 CET 2006

The problem has been solved and thankfully, it has nothing to do with Quartz and 
almost nothing to do with R. Before explaining briefly, I want to thank Kevin 
Middleton, Don MacQueen, and Jim Holtman for offering their help. This kind of 
support makes using tools like R even better (especially for newbies like me).

It turns out that the problem had to do with the format of the data being used 
to generate the plots. Although I didn't mention it in my question, the data was 
being read in from a formatted file (produced by someone other than me). One of 
the things I found impressive about R was the ease with which it read in the 
file. That reaction was based, in part, on being a Mathematica user and having 
struggled more to get it to read the same file on an earlier occasion. That may 
not have been such a bad thing after all.

Don MacQueen was the one who asked the right questions that led to me reveal the 
file format as:
Date     Value
00-03-27 129622
00-03-28 129285
00-03-29 141328
00-03-30 130223

He immediately recognized that the "Date" column was going to cause trouble 
unless R was given more explicit instructions about how to treat it viz., as a 

In lieu of that (and this is the not so good part), R decides to be "helpful" 
and treat that column as integers. Probably (I haven't done the detailed 
analysis) that led to each triple of integers being computed as a pair (the 00- 
being treated as a zero) which led to each "dot" in the plot being displayed as 
a pair of dots, with further confusion apparently causing R to render the "dots" 
as  something more complex (e.g., "knots"). You get the idea.

Whether to interpret certain values as numbers or strings is an old I/O gotcha.
What had me fooled was that the plot *looked* correct, when compared to the 
Mathematica plot, but it was taking far too much time to render on PPC Quartz!


Neil Gunther wrote:
> I just tried rendering a plot of 166 data point (time series) on my PPC 
> mac,
> and compared it with the same data rendered by Mathematica. The R 
> plotting is very slow to paint and repaint, compared to Mathematica. 
> This also makes it extremely awkward to use in other documentation such 
> as pdfLatex.
> On closer inspection, it looks like the Mathematica plot is just a 
> polyline, while in R it is a B-spline with each marker consisting of 24 
> B-splines knotted together. Moreover, the spline joints are rounded, 
> which requires computing two circles and intersecting them 26 times at 
> each bend.
> Is there some reason why the point-markers are not just drawn as circles 
> or squares, instead of doing these complicated and time-consuming knots?
> -- njg
> ________________________________________________________________________
> PERFORMANCE DYNAMICS COMPANY               http://www.perfdynamics.com/
> ________________________________________________________________________

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