break exit script

Question

I have a program that does some data analysis and is a few hundred lines long     Very early on in the program  I want to do some quality control and if there is not enough data  I want the program to terminate and return to the R console  Otherwise  I want the rest of the code to execute   I ve tried break browser  and quit and none of them stop the execution of the rest of the program  and quit stops the execution as well as completely quitting R  which is not something I want to happen   My last resort is creating an if-else statement as below    if n  lt  500     else  insert rest of program here     but that seems like bad coding practice   Am I missing something

User · Answer

This is an old question but there is no a clean solution yet. This probably is not answering this specific question, but those looking for answers on 'how to gracefully exit from an R script' will probably land here. It seems that R developers forgot to implement an exit() function. Anyway, the trick I've found is:

continue <- TRUE

tryCatch({
     # You do something here that needs to exit gracefully without error.
     ...

     # We now say bye-bye         
     stop("exit")

}, error = function(e) {
    if (e$message != "exit") {
        # Your error message goes here. E.g.
        stop(e)
    }

    continue <<-FALSE
})

if (continue) {
     # Your code continues here
     ...
}

cat("done.\n")

Basically, you use a flag to indicate the continuation or not of a specified block of code. Then you use the stop() function to pass a customized message to the error handler of a tryCatch() function. If the error handler receives your message to exit gracefully, then it just ignores the error and set the continuation flag to FALSE.

User · Answer

Reverse your if-else construction   if n  gt   500        do stuff     no need for else

User · Answer

You can use the pskill function in the R  tools  package to interrupt the current process and return to the console  Concretely  I have the following function defined in a startup file that I source at the beginning of each script  You can also copy it directly at the start of your code  however  Then insert halt   at any point in your code to stop script execution on the fly  This function works well on GNU Linux and judging from the R documentation  it should also work on Windows  but I didn t check      halt  interrupts the current R process  a short iddle time prevents R from   outputting further results before the SIGINT    Ctrl-C  signal is received  halt  lt - function hint    Process stopped  n         writeLines hint      require tools  quietly   TRUE      processId  lt - Sys getpid        pskill processId  SIGINT      iddleTime  lt - 1 00     Sys sleep iddleTime

User · Answer

Edit  Seems the OP is running a long script  in that case one only needs to wrap the part of the script after the quality control with  if  n  gt   500          long running code here      If breaking out of a function  you ll probably just want return    either explicitly or implicitly   For example  an explicit double return  foo  lt - function x      if x  lt  10        return NA      else       xx  lt - seq len x      xx  lt - cumsum xx        xx    return xx  is implied here     gt  foo 5   1  0  gt  foo 10    1   1  3  6 10 15 21 28 36 45 55   By return   being implied  I mean that the last line is as if you d done return xx   but it is slightly more efficient to leave off the call to return     Some consider using multiple returns bad style  in long functions  keeping track of where the function exits can become difficult or error prone  Hence an alternative is to have a single return point  but change the return object using the if    else    clause  Such a modification to foo   would be  foo  lt - function x         out is NA or cumsum xx  depending on x   out  lt - if x  lt  10        NA     else       xx  lt - seq len x      cumsum xx        out    return out  is implied here     gt  foo 5   1  NA  gt  foo 10    1   1  3  6 10 15 21 28 36 45 55

User · Answer

Here   if n  lt  500          quit         or        stop  this is some message     else        insert rest of program here      Both quit   and stop message  will quit your script  If you are sourcing your script from the R command prompt  then quit   will exit from R as well

User · Answer

Not pretty  but here is a way to implement an exit   command in R which works for me   exit  lt - function        Internal  invokeRestart list NULL  NULL   NULL      print  this is the last message   exit   print  you should not see this     Only lightly tested  but when I run this  I see this is the last message and then the script aborts without any error message

User · Answer

You could use the stopifnot   function if you want the program to produce an error   foo  lt - function x        stopifnot x  gt  500        rest of program

User · Answer

Perhaps you just want to stop executing a long script at some point  ie  like you want to hard code an exit   in C or Python   print  this is the last message   stop   print  you should not see this

[r] break/exit script

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