[R] Plotting does odd line thing

[Marc Girondot]

Le 08/04/2014 04:20, David Doyle a écrit :
> Hello folks,
>
> When I use the lines function below it connects all my points but then
> draws a line back to the start point.  Any suggestions on what is going on??
>
> mydata <-read.csv("http://doylesdartden.com/R/test_data.csv", sep=",")
>
> attach(mydata)
>
> plot(EMD~Year,data=mydata, subset = Well.ID %in% c("MW-1", "D_EMD"),
> col=ifelse(D_EMD, "black", "red"), pch=ifelse(D_EDM, 19, 17), cex = 1.5)
>
> lines(EMD~Year)
>
> Thank you for your time.
>
> David
>
>
First, there is a typo error here:

pch=ifelse(D_EMD, 19, 17)

Second try this to see that year data are not monotonically increasing. 
Then it produces the zig-zag effect that you observe:
plot(1990:2000, c(rep(0, 10), 10), type="n")
lines(EMD~Year)
It can be seen here also:
diff(Year)
or
diff(Year)<0

Sincerely,

Marc