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I am trying to pause my code for a little while, time for me to observe the plots.

I tried:

print('A')
something = readline("Press Enter")
print('B')
print('C')

, then there is no pause, the line print('B') is fed to readline and get stored into something and therefore only A and C got printed on the screen. Note that if I add an empty line between Something = readline("Press Enter") and print("B"), then print("B") get printed on the screen but still the console doesn't allow the user to press enter before continuing.

And I tried:

print('A')
Sys.sleep(3)
print('B')
print('C')

The program waits 3 seconds before starting and then run "normally" without doing any pause between print('A') and print('B').

What do I missunderstand?

Here is my R version: R 3.1.1 GUI 1.65 Snow Leopard build (6784)

Remi.b
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  • If you are copy/pasting to the R console the first block, you actually press enter while doing it (there is a newline character at the end of each line). I can't reproduce what you got for the second block (system actually stops after the first line). – nicola Nov 04 '14 at 19:14

1 Answers1

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The problem with readline is that if you paste your script into an R console, or execute it from eg Rstudio, the redline function is read and then the next line of the script is read in as the console entry, which in your case sets the value of something to print('B).

An easy way to get around this is to stick your entire code in a function, then call the function to run it. So, in your case:

myscript = function(){

  print('A')
  something = readline(prompt = "Press Enter")
  print('B')
  print('C')

}

myscript()

The output of this for me (in Rstudio, with R version 3.1.1):

[1] "A"
Press Enter
[1] "B"
[1] "C"

This has always felt like a bit of a hack to me, but it's essentially what the readline documentation recommends in its example.

I've never used sleep in my code, so I can't help you there.

Edit to clarify based on comments: This will only work if myscript() is the very last line of your script, or if it is manually entered into the console after running the script to generate the function. Otherwise, you will run into the same problem as before- the next line of code will be automatically entered.

Joe
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  • Oh..This is so weird! You definitely solved my issue, thank you! Yet, I don't really understand why wrapping the entire code in a function makes `readline` works as I wish it to. – Remi.b Nov 04 '14 at 19:20
  • If `readline` is called from a function _at the very end of your script_, you aren't reading more lines of code immediately after it, and R will actually wait for your input. To experiment with this, try running your original script line by line, or running the script from my answer with a `#comment` after the last line. – Joe Nov 04 '14 at 19:31