[Rd] example() and "ask"

[Gavin Simpson]

Dear list,

Is it intentional that example() opens a new device and leaves it in a
mode where it asks (prompts) the user to Press return to see the next
plot for *all* subsequent plots on that device.

For example; with an already opened device, example() works as I would
expect:

> par("ask")
[1] FALSE
> example(lm)
.... OUTPUT CLIPPED ....
lm> plot(lm.D9, las = 1)      # Residuals, Fitted, ...
Hit <Return> to see next plot: 

lm> par(opar)

lm> ## model frame :
lm> stopifnot(identical(lm(weight ~ group, method = "model.frame"),
lm+                     model.frame(lm.D9)))
> plot(1:10)
>

So with an already opened device, plots /within/ example prompt the user
(by default) but at the end of the example, we return to default and we
are not prompted to display subsequent plots on that device (par("ask)
== FALSE)

However, if example opens a device (i.e. example is the first plotting
function called in a session), then the device remains in "prompt" mode:

> # continue example from above, so close the device
> dev.off()
null device 
          1 
> example(lm) # will open device when required
.... output suppressed ....
lm> plot(lm.D9, las = 1)      # Residuals, Fitted, ...
Hit <Return> to see next plot: 

lm> par(opar)

lm> ## model frame :
lm> stopifnot(identical(lm(weight ~ group, method = "model.frame"),
lm+                     model.frame(lm.D9)))
> par("ask")
[1] TRUE
> plot(1:10)
Hit <Return> to see next plot: 

Device remains in "prompt" mode.

I would have expected example() to clean up and return par("ask") to
what it was before example() was called in the case where it opens it's
own device, just as it does if called with an already open and active
device.

If this is intentional, it doesn't strike me as being intuitive or user
friendly. Is there scope and a will to change this behaviour?

This is with R 2.7.1RC and R 2.8.0 to be:

> version
               _                                     
platform       x86_64-unknown-linux-gnu              
arch           x86_64                                
os             linux-gnu                             
system         x86_64, linux-gnu                     
status         RC                                    
major          2                                     
minor          7.1                                   
year           2008                                  
month          06                                    
day            16                                    
svn rev        45948                                 
language       R                                     
version.string R version 2.7.1 RC (2008-06-16 r45948)

> version
               _                                                               
platform       x86_64-unknown-linux-gnu                                        
arch           x86_64                                                          
os             linux-gnu                                                       
system         x86_64, linux-gnu                                               
status         Under development (unstable)                                    
major          2                                                               
minor          8.0                                                             
year           2008                                                            
month          06                                                              
day            18                                                              
svn rev        45948                                                           
language       R                                                               
version.string R version 2.8.0 Under development (unstable) (2008-06-18 r45948)

Many thanks,

G
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 Dr. Gavin Simpson             [t] +44 (0)20 7679 0522
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