R help - Jan 2014 - xyplots in lattice - strange behaviour, possible bug?

Hello everyone,

I'm very green on R,  I'm following a Coursera course about it when I
hit a problem when I rewrote the same code the professor use in the
lecture.
I'm running Win 7 x64, R 3.0.2 x64 and the last version of Rstudio IDE

 I put up this script:


library(lattice)
x <- rnorm (100)
z <- x + rnorm(100)
f <- gl(2,50,labels =c("Groups 1" , "Groups 2"))
xyplot (z ~ x | f,
        panel = function (x, z, ...) {
          panel.xyplot(x,z, ...)
          panel.abline(h = median(z),
                       lty=2
                       )})


In my box don't work, it give no error in the terminal, the plotting
windonw will be opened, the graphbox drawed with all the ticks and the
titles as intended but instead of the actual data plot inside the
graph I have this error "Error using packet <x> argment "z"
is
missing, with no default" where <x> is 1 or 2 as the script draw two
graphs.

I reported this behaviour in the lecture forum and someone replicated it.

I replicated this behaviour even with R alone running the above script
with the same results.

If I call traceback() no value is given, there is no traceback.

Apparently not everyone could replicate this behaviour for some reason.

As you could see the code must work but didn't.

A similar thing happens if I change the part after the function with
another like:

... <same code of above>...
 panel= function(x,y, ...) {
          panel.xyplot(x,z, ...)
          fit <- lm(y~x)
          panel.abline(fit)
        })

but don't happens if I call a xyplot without calling a function in it.

Have any ideas?

Well, if the professor wrote that, it wouldn't have run for him
either! You need to take better notes.

What's going on: You need to distinguish between formal and actual
arguments.
?panel.xyplot
tells you that the formal arguments for this function are x,**y** ,...
 (emphasis added) and NOT x,**z**,...

The **actual** argument for y passed to the function will be z. So
change your "z" to a "y" in your function call and it will
run:

library(lattice)
x <- rnorm (100)
z <- x + rnorm(100)
f <- gl(2,50,labels =c("Groups 1" , "Groups 2"))
xyplot (z ~ x | f,
        panel = function (x, y, ...) {
          panel.xyplot(x,y, ...)
          panel.abline(h = median(y),
                       lty=2
                       )})


Cheers,
Bert

Bert Gunter
Genentech Nonclinical Biostatistics
(650) 467-7374

"Data is not information. Information is not knowledge. And knowledge
is certainly not wisdom."
H. Gilbert Welch




On Wed, Jan 22, 2014 at 2:10 PM, Manlio Calvi <manlio.calvi at gmail.com>
wrote:
> Hello everyone,
>
> I'm very green on R,  I'm following a Coursera course about it when
I
> hit a problem when I rewrote the same code the professor use in the
> lecture.
> I'm running Win 7 x64, R 3.0.2 x64 and the last version of Rstudio IDE
>
>  I put up this script:
>
>
> library(lattice)
> x <- rnorm (100)
> z <- x + rnorm(100)
> f <- gl(2,50,labels =c("Groups 1" , "Groups 2"))
> xyplot (z ~ x | f,
>         panel = function (x, z, ...) {
>           panel.xyplot(x,z, ...)
>           panel.abline(h = median(z),
>                        lty=2
>                        )})
>
>
> In my box don't work, it give no error in the terminal, the plotting
> windonw will be opened, the graphbox drawed with all the ticks and the
> titles as intended but instead of the actual data plot inside the
> graph I have this error "Error using packet <x> argment
"z" is
> missing, with no default" where <x> is 1 or 2 as the script draw
two
> graphs.
>
> I reported this behaviour in the lecture forum and someone replicated it.
>
> I replicated this behaviour even with R alone running the above script
> with the same results.
>
> If I call traceback() no value is given, there is no traceback.
>
> Apparently not everyone could replicate this behaviour for some reason.
>
> As you could see the code must work but didn't.
>
> A similar thing happens if I change the part after the function with
> another like:
>
> ... <same code of above>...
>  panel= function(x,y, ...) {
>           panel.xyplot(x,z, ...)
>           fit <- lm(y~x)
>           panel.abline(fit)
>         })
>
> but don't happens if I call a xyplot without calling a function in it.
>
> Have any ideas?
>
> ______________________________________________
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> 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.