[R] Can't add error bars to existing line graph

[John Fox]

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
> 
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