[R] problem with the behaviour of dashed lines in R plots

[jean-philippe]

dear R users,

I am performing a linear regression with lm, and I would like to plot 
the regressor in dashed lines. I know that the lty=2 option is the way 
out, but it has a very strange behaviour: the line starts dashed but 
then the spaces between each dash becomes very tiny and so the line 
become somehow continuous for the human eye. Do you know how to fix that 
problem, in order to have a dashed line with big enough spaces between 
the dashes?
Here is a MWE (don't mind if clearly a linear model will not fit these 
"fake randomly generated" data).

Also, changing the plot(...,type="l") to abline(regressor,lty=2,...) 
helps and draw a pure dashed line but it is impossible to force it to 
stay in the bounds of the data.
Changing to line instead shows the same problem as mentioned here in the 
MWE.


pdf("reproducableex.pdf")
df1<-data.frame(B=runif(20,1.4,1.6),A=runif(20,-19.5,-9.8))
regressor<-lm(A~B,data = df1)
plot(df1$B,predict(regressor,df1),type="l", col="black", 
mgp=c(2,0.5,0),cex.lab=1.6, lwd=2, 
lty=2,xlim=range(c(1.2,1.7)),ylim=rev(range(c(-19,-8))))
par(new = TRUE)
plot(df1$B,as.numeric(df1$A),type="p", col="black", 
mgp=c(2,0.5,0),cex.lab=1.6,cex=2, xlab = "", ylab = 
"",xlim=range(c(1.2,1.7)),ylim=rev(range(c(-19,-8))),pch=17)
box(lwd=3)
dev.off()


Thanks in advance, best regards


Jean-Philippe Fontaine

-- 
Jean-Philippe Fontaine
PhD Student in Astroparticle Physics,
Gran Sasso Science Institute (GSSI),
Viale Francesco Crispi 7,
67100 L'Aquila, Italy
Mobile: +393487128593, +33615653774