readLines function with new version of R

Question

My function is:

create_matrix <- function() {
  cat("Write the numbers of vertices: ")
  user_input <- readLines("stdin", n=1)
  user_input <- as.numeric(user_input)
  print(user_input)
  }

With the version 3.5.0, after i entered the data the program doesn't continue the execution. I'm calling the script directly from the console.

Deliciadelicious

Can't you use data = readLines(n=1)? – Polly

Yes, but it doesn't work – Deliciadelicious

The Note in help("showConnections") might be relevant: " GUI consoles (which may not have an active ‘stdin’, and if they do it may not be connected to console input)". – Polly

What does "doesn't work" mean specifically? – Polly

Sorry, it continue the execution but it doesn't wait my input and it give me NA value. – Deliciadelicious

Can you add some more details, in particular regarding how you "entered the data" with Rscript? If you can improve this question I'd consider attaching a bounty to it because I think it might be an interesting problem. – Polly

First of all, i launch the script named graphi.R directly from terminal with an argument (for example graphi.R -c, to create a matrix(i'm using the argparse library for that)). The function create_matrix is called and ask me the number of vertices in my console. After i entered the number it's like it's waiting for another input (like a loop). With the older version i hadn't problem, i notice that they changed something in the readLines function. Thanks for your help. – Deliciadelicious

Please edit this information (with the actual code and a minimal example of a script) into the question. – Polly

I updated the question. So, i can confirm that the script works fine with the version 3.4.4_2. – Deliciadelicious

The is a bug fix in R-patched concerning seekable streams and stdin so you may be hitting that. – Weald

See also this: github.com/wch/r-source/blob/trunk/doc/NEWS.Rd#L113 – Polly

Thanks for your help, i understand the problem but i don't know how to solve it. So i'm back to the previous version. – Deliciadelicious

@Deliciadelicious Can you post your Operating system type, version and rsession info? That should help a lot. i.e Are you on MacOSX, Windows or Unix OS. stdin has different properties across Windows and various flavors of Unix. – Halftrack

I'm currently on arch. – Deliciadelicious

Given the answer below, it is probably worth reporting this to R-devel. – Judgment

@DirkEddelbuettel : No, that bug fix in R-patched does not fix the problem. But using stdin() {much more expressive anyway}, does work in all versions of R (see my A below). – Reviviscence

Answer 1

My findings using various docker images:

• The example works fine using R version 3.4.4 (2018-03-15) -- "Someone to Lean On" from rocker/r-ver:3.4.4.
• The example hangs as described using R version 3.5.0 (2018-04-23) -- "Joy in Playing" from rocker/r-ver:3.5.0.
• The example hangs as described using R Under development (unstable) (2018-05-19 r74746) -- "Unsuffered Consequences" from rocker/drd.

It looks as if the change mentioned in the release notes for version 3.5.1 is unrelated. I have sent my findings to r-devel and will report back the outcome:

• The example works fine using R version 3.5.1 (2018-07-02) -- "Feather Spray"

• The bug has been marked as fixed. I can assert that version R Under development (unstable) (2018-06-02 r74838) -- "Unsuffered Consequences" works as expected.

• This is considered a bug, but it's unclear how and when it will be fixed.

• A reasonable workaround: Send end-of-file (EOF, Ctrl-D) in addition to end-of-line.

Garlaand

can you share you docker script? – Halftrack

@Halftrack All the docker images are available on docker hub via the rocker project. Anything else you are interested in? – Garlaand

Thanks, based on the note I had presumed you had written a docker script that downloaded an image and then ran the code. If not no worries. – Halftrack

Answer 2

TLDR: Use stdin()

It works fine if you use stdin() instead of "stdin" .... which we would have recommended anyway.

But probably, for back compatibility "stdin" should probably work too ((or then signal a deprecation warning and work for now)

Provinciality

stdin() works in an interactive session, but not when the script is started from the console. Your first suggestion on r-devel (send EOF / Ctrl-D) works fine. – Garlaand

You are right, and I was wrong above: stdin() is not usable in a script, just interactively. – Reviviscence