[R] Potential bug in readLines when reading empty lines

[Heuvel, E.G. van den (Guido)]

-----Oorspronkelijk bericht-----
Van: Enrico Schumann <es using enricoschumann.net> 
Verzonden: woensdag 25 juni 2025 16:44
Aan: Heuvel, E.G. van den (Guido) <g.vandenheuvel using cbs.nl>
CC: 'r-help using R-project.org' <r-help using r-project.org>
Onderwerp: Re: [R] Potential bug in readLines when reading empty lines

[Externe email]


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

My preferred rule would be the current documentation of the readLines function. Specifically, the line "Whatever mode the connection is opened in, any of LF, CRLF or CR will be accepted as the EOL marker for a line."