Hi, Sarah's last comment about using min/max x got me thinking. It's not that the points are "very close together", it's that the x-values are not ordered. So the plot is actually drawing a dashed line back-and-forth between different points on the line, which has the effect of making the result appear non-dashed. If you sort by the x-values before plotting you will see the output is very different. I am not saying this is a better solution than Sarah's regarding just using the end-points, but at least it partially explains the relevance of that suggestion.
For example, here is a slightly modified version of the code that does an ordering before plotting: df1<-data.frame(B=runif(20,1.4,1.6),A=runif(20,-19.5,-9.8)) regressor<-lm(A~B,data = df1) df2 <- data.frame( x=df1$B, yhat= predict(regressor,df1)) df2 <- df2[ order(df2$x), ] plot(df2$x,df2$yhat,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) HTH, Eric On Mon, Dec 4, 2017 at 8:30 PM, jean-philippe < jeanphilippe.fonta...@gssi.infn.it> wrote: > hi Sarah, > > Thanks a lot for having taken time to answer me and for your reply. I > wonder how I missed this solution. Indeed plotting the line with the 2 > extreme data points works perfectly. > > > Best, > > > Jean-Philippe Fontaine > > > > On 04/12/2017 18:30, Sarah Goslee wrote: > >> It's because you are plotting a line between each of the points in >> your data frame, and they are very close togethe >> > > -- > Jean-Philippe Fontaine > PhD Student in Astroparticle Physics, > Gran Sasso Science Institute (GSSI), > Viale Francesco Crispi 7, > 67100 L'Aquila, Italy > Mobile: +393487128593, +33615653774 > > ______________________________________________ > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posti > ng-guide.html > and provide commented, minimal, self-contained, reproducible code. > [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.