Dear Bruno, There are (at least) two errors here: (1) I think that you misunderstand how interaction.plot(), and more generally R base graphics, work. interaction.plot() doesn't return a graphics object, but rather draws on a graphics device as a side effect. Of course, interaction.plot() is a function and so it must return something -- it invisibly returns NULL. (2) I assume that you independently computed Scaphmeans and Scaphse, although you didn't include the corresponding code in your message. In any event, the arrows() function generally takes 4 arguments (x0, y0, x1, y1), specifying the x and y coordinates of the endpoints of the arrows. It's true that because your "arrows" are intended to be vertical, you need not specify x1, which defaults to x0, but the other 3 arguments are necessary. See ?arrows for details. I hope this helps, John John Fox, Professor Emeritus McMaster University Hamilton, Ontario, Canada web: https://socialsciences.mcmaster.ca/jfox/ On 2021-06-15 9:02 a.m., Bruno.Salonen wrote:> > Hi all, > > I'm trying to add error bars to an existing line graph in base R. > > The basic line graph comes up just fine, but it does not show my error > bars... > > Data frame = readscaphfileNEW > Plot name = SCAPHLINEGRAPHNEW > x axis = TEMP > y axis = SCAPH.BPM > Tracer = Year (SAME AS 'EXPERIMENT) > Scaphmeans = means of SCAPH.BPM > Scaphse = standard error of SCAPH.BPM > > Here is the code.. > > SCAPHLINEGRAPHNEW <- interaction.plot(readscaphfileNEW$TEMP, > readscaphfileNEW$EXPERIMENT, readscaphfileNEW$SCAPH.BPM, > xlab = "Temperature (?C)", ylab = "Scaphognathite Rate (BPM)", > main = "Scaphognathite", > ylim = c(0,300), trace.label = "Year", > type = "b", pch = c(19,17), fixed = TRUE) > arrows(SCAPHLINEGRAPHNEW,Scaphmeans+Scaphse,SCAPHLINEGRAPHNEW,Scaphmeans-Scaphse,code=3, > angle=90, length=0.1) > > Why are my error bars not showing? Is the 'arrows' line wrong? > > Thanks a million for your help, everybody. > > Here is my data set: > >> readscaphfileNEW > EXPERIMENT TEMP SCAPH.BPM > 1 2021 12 82 > 2 2021 12 58 > 3 2021 12 78 > 4 2021 12 59 > 5 2021 12 80 > 6 2021 12 100 > 7 2021 12 61 > 8 2021 12 103 > 9 2021 12 61 > 10 2021 17 100 > 11 2021 17 70 > 12 2021 17 83 > 13 2021 17 73 > 14 2021 17 143 > 15 2021 17 103 > 16 2021 17 73 > 17 2021 17 158 > 18 2021 17 95 > 19 2021 17 80 > 20 1939 12 158 > 21 1939 12 148 > 22 1939 12 152 > 23 1939 12 148 > 24 1939 12 160 > 25 1939 12 168 > 26 1939 12 152 > 27 1939 12 150 > 28 1939 12 187 > 29 1939 17 300 > 30 1939 17 302 > 31 1939 17 291 > 32 1939 17 240 > 33 1939 17 253 > 34 1939 17 207 > 35 1939 17 184 > 36 1939 17 224 > 37 1939 17 242 > 38 1939 17 236 > > Bruno > > > > -- > Sent from: https://r.789695.n4.nabble.com/R-help-f789696.html > > ______________________________________________ > R-help at 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. >