R devel - Dec 2007 - capture.output(), truncated last output without \n (PR#10534)

Full_Name: Philippe Grosjean
Version: 2.6.1
OS: MacOS X; Windows XP
Submission from: (NULL) (81.243.237.235)


Last output from capture.output() is truncated if it does not end with a
carriage return:
> capture.output(cat("text\n"))  # Fine
[1] "text"
> capture.output(cat("text"))    # Missing output!
character(0)
> capture.output({cat("text");1+1})  # Only last output is affected
[1] "text[1] 2"

Proposed patch: add a carriage return before exiting capture.output():

capture.output <-
function (..., file = NULL, append = FALSE) {

    
[...]

        for (item in tmp) if (item$visible) 
            print(item$value)
    }
    cat("\n")  ### ADD THIS!
    rval
}

This changes the behavior of capture.output() a little bit, since it adds
"" at
the end of regular outputs, but it solves the problem and it allows to detect if
last output line was ended by \n, or not.

Regards,

Philippe Grosjean
               _                           
platform       i386-apple-darwin8.10.1     
arch           i386                        
os             darwin8.10.1                
system         i386, darwin8.10.1          
status                                     
major          2                           
minor          6.1                         
year           2007                        
month          11                          
day            26                          
svn rev        43537                       
language       R

Thank you, Brian.

Prof Brian Ripley wrote:
> This only happens if 'file' is a text connection, and is the
expected
> behaviour in that case: you cannot capture an incomplete line to a text 
> connection.
Well, in ?textConnection, Details section, one can read:
"Closing the connection will output the final line, complete or not."
> There seems no reason to break the documented behaviour in other cases 
> to change something that you consider to a bug when file=NULL and the 
> user does not produce complete output.  It would be possible to make use 
> of isIncomplete() to add a final newline only where needed to complete a 
> line.  E.g. use
> 
>     if(inherits(file, "textConnection") &&
isIncomplete(file)) cat("\n")
This is fine, except one cannot detect when the last line was complete 
or not in capture.output(). I suggest adding an attribute complete = 
TRUE/FALSE to the result returned by capture.output(), or any other mean 
to return this information.

Best,

Philippe Grosjean
> 
> On Sat, 29 Dec 2007, phgrosjean at sciviews.org wrote:
> 
>> Full_Name: Philippe Grosjean
>> Version: 2.6.1
>> OS: MacOS X; Windows XP
>> Submission from: (NULL) (81.243.237.235)
>>
>>
>> Last output from capture.output() is truncated if it does not end with
a
>> carriage return:
>>
>>> capture.output(cat("text\n"))  # Fine
>> [1] "text"
>>> capture.output(cat("text"))    # Missing output!
>> character(0)
>>> capture.output({cat("text");1+1})  # Only last output is
affected
>> [1] "text[1] 2"
>>
>> Proposed patch: add a carriage return before exiting capture.output():
>>
>> capture.output <-
>> function (..., file = NULL, append = FALSE) {
>>
>>
>> [...]
>>
>>        for (item in tmp) if (item$visible)
>>            print(item$value)
>>    }
>>    cat("\n")  ### ADD THIS!
>>    rval
>> }
>>
>> This changes the behavior of capture.output() a little bit, since it 
>> adds "" at
>> the end of regular outputs, but it solves the problem and it allows to 
>> detect if
>> last output line was ended by \n, or not.
>>
>> Regards,
>>
>> Philippe Grosjean
>>               _
>> platform       i386-apple-darwin8.10.1
>> arch           i386
>> os             darwin8.10.1
>> system         i386, darwin8.10.1
>> status
>> major          2
>> minor          6.1
>> year           2007
>> month          11
>> day            26
>> svn rev        43537
>> language       R
>>
>> ______________________________________________
>> R-devel at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-devel
>>
>