[R] Potential bug in readLines when reading empty lines

[Enrico Schumann]

Quoting "Heuvel, E.G. van den (Guido) via R-help" <r-help using r-project.org>:

> Hi all,
>
> I encountered some weird behaviour with readLines() recently, and I  
> am wondering if this might be a bug, or, if it is not, how to  
> resolve it. The issue is as follows:
>
> If I have a text file where a line ends with just a carriage return  
> (\r, CR) while the next line is empty and ends in a carriage return  
> / linefeed (\r\n, CR LF), then the empty line is skipped when  
> reading the file with readLines. The following code contains a test  
> case:
>
> ---
> print(R.version)
> # platform       x86_64-w64-mingw32
> # arch           x86_64
> # os             mingw32
> # crt            ucrt
> # system         x86_64, mingw32
> # status
> # major          4
> # minor          4.0
> # year           2024
> # month          04
> # day            24
> # svn rev        86474
> # language       R
> # version.string R version 4.4.0 (2024-04-24 ucrt)
> # nickname       Puppy Cup
>
> txt_original <- paste0("Line 1\r", "\r\n", "Line 3\r\n")
>
> # Write txt_original as binary to avoid unwanted conversion of end  
> of line markers
> writeBin(charToRaw(txt_original), "test.txt")
>
> txt_actual <- readLines("test.txt")
> print(txt_actual)
> # [1] "Line 1" "Line 3"
>  ---
>
> I included the output of this script on my machine in the comments.  
> I would expect txt_actual to be equal to c("Line 1", "", "Line 3"),  
> but the empty line is skipped.
>
> Is this a bug? And if not, how should I read test.txt in such a way  
> that the empty 2nd line is left intact?
>
> Best regards,
>
> Guido van den Heuvel
> Statistics Netherlands

What would be your "rule" for identifying lines? From your desired output,
it seems \r should be end-of-line, and \n is to be ignored. Then you could
do something like that:

   raw <- readChar("test.txt", 1000)
   raw <- gsub("\n", "", raw)
   strsplit(raw, "\r")[[1]]
   ## [1] "Line 1" ""       "Line 3"

But it requires you to specify the number of characters to read (or write a
loop).


-- 
Enrico Schumann
Lucerne, Switzerland
https://enricoschumann.net