Telling a Loop to "Skip" an Iteration if it Takes Too Long-CodePudding

I have this code in R:

output = list()

for (i in 1:999) 

{tryCatch({

{

    link_i<-  paste0(www.some_website, i 1,  /some_extension/, i,  .com)

    material_i <-  fromJSON(link_i)





   output[[i]] <- material_i

}

   }, error = function(e){})

}

Due to the nature of the code I am running, I have noticed that sometimes this loop gets "stuck" on a specific iteration. For instance, this loop might get stuck on the 45th iteration and take a very long time.

I am looking for some mechanism to tell the computer that "if more than x seconds is spent on a certain iteration, skip to the next iteration".

I found this function over here that might be useful : https://www.rdocumentation.org/packages/R.utils/versions/2.11.0/topics/withTimeout - but I am not sure if this is the correct function to use for such a task.

Can someone please recommend something and please show me how to use it?

Thank you!

CodePudding user response：

The function you linked to seems quite appropriate to me (but I've never used it). Here's an example with a function foo() that is quite fast for all inputs except when x = 5 where it takes 5 seconds to run.

suppressPackageStartupMessages(library(R.utils))

# function that is fast except when x = 5
foo <- function(x) {
  if (x == 5) {
    Sys.sleep(5)
  } else {
    Sys.sleep(0.5)
  }
  return(x)
}

# create a list to store the results
res <- vector("list", length = 10L)

# Make a loop where we try to store the result of each iteration. If iteration
# takes more than 1 sec, then skip it.
for (i in 1:10) {
  print(i)
  tryCatch({
    res[[i]] <- withTimeout({
      foo(i)
    }, timeout = 1)
  }, TimeoutException = function(ex) {
    message("Timeout. Skipping.")
    res[[i]] <- NULL
  })
}
#> [1] 1
#> [1] 2
#> [1] 3
#> [1] 4
#> [1] 5
#> Timeout. Skipping.
#> [1] 6
#> [1] 7
#> [1] 8
#> [1] 9
#> [1] 10

res
#> [[1]]
#> [1] 1
#> 
#> [[2]]
#> [1] 2
#> 
#> [[3]]
#> [1] 3
#> 
#> [[4]]
#> [1] 4
#> 
#> [[5]]
#> NULL
#> 
#> [[6]]
#> [1] 6
#> 
#> [[7]]
#> [1] 7
#> 
#> [[8]]
#> [1] 8
#> 
#> [[9]]
#> [1] 9
#> 
#> [[10]]
#> [1] 10

^{Created on 2022-09-16 with reprex v2.0.2}