R help - Jun 2011 - lines(..., lwd=3) inaccuracy

Using a line width > 1 results in not only a thicker line but also some fuzz
in the other direction, as shown in this example program.  You will see that
the thick vertical black lines extend below the gray scale horizontal lines. 
Does anyone know whether this is intended or is it a bug?  The application
is for displaying a correlation matrix (here just some random U(0,1)s). 
Thanks -Frank


par(mar=c(1,2,0,0), xpd=NA)
set.seed(1)
r <- matrix(runif(16), nrow=4, dimnames=list(NULL, paste('x', 1:4,
sep='')))
p <- nrow(r)
v <- colnames(r)
plot(c(-.35,p+.5),c(.5,p+.25), type='n', axes=FALSE,
     xlab='',ylab='')
text(rep(.5,p), 1:p, v, adj=1)
maxabsr <- max(abs(r[row(r) != col(r)]))
for(i in 1:p) {
  for(j in 1:p) {
    if(i >= j) next
    lines(c(i,i),c(j,j+r[i,j]/maxabsr/2), lwd=3)
    lines(c(i-.2,i+.2),c(j,j), col=gray(.7))
  }
  text(i, i, v[i], srt=-45, adj=0)
}


-----
Frank Harrell
Department of Biostatistics, Vanderbilt University
--
View this message in context:
http://r.789695.n4.nabble.com/lines-lwd-3-inaccuracy-tp3603375p3603375.html
Sent from the R help mailing list archive at Nabble.com.

Hi Frank,

It's not inaccuracy, exactly, and it's intentional.

The default behavior is to use a round endcap on a line, and with such
a large linewidth that endcap is arcing below and above the starting
points.

This being R, there's a par for that: putting lend=1 in your lines()
statements will give you the result you're looking for.

Sarah

On Thu, Jun 16, 2011 at 3:03 PM, Frank Harrell <f.harrell at
vanderbilt.edu> wrote:
> Using a line width > 1 results in not only a thicker line but also some
fuzz
> in the other direction, as shown in this example program. ?You will see
that
> the thick vertical black lines extend below the gray scale horizontal
lines.
> Does anyone know whether this is intended or is it a bug? ?The application
> is for displaying a correlation matrix (here just some random U(0,1)s).
> Thanks -Frank
>
>
> par(mar=c(1,2,0,0), xpd=NA)
> set.seed(1)
> r <- matrix(runif(16), nrow=4, dimnames=list(NULL, paste('x',
1:4, sep='')))
> p <- nrow(r)
> v <- colnames(r)
> plot(c(-.35,p+.5),c(.5,p+.25), type='n', axes=FALSE,
> ? ? xlab='',ylab='')
> text(rep(.5,p), 1:p, v, adj=1)
> maxabsr <- max(abs(r[row(r) != col(r)]))
> for(i in 1:p) {
> ?for(j in 1:p) {
> ? ?if(i >= j) next
> ? ?lines(c(i,i),c(j,j+r[i,j]/maxabsr/2), lwd=3)
> ? ?lines(c(i-.2,i+.2),c(j,j), col=gray(.7))
> ?}
> ?text(i, i, v[i], srt=-45, adj=0)
> }
>
>

-- 
Sarah Goslee
http://www.functionaldiversity.org