CODEWITHSUNDEEP
rloopstry-catchredo
RPO
RPO

Reputation: 129

How to redo tryCatch after error in for loop

I am trying to implement tryCatch in a for loop.

The loop is built to download data from a remote server. Sometimes the server no more responds (when the query is big).

I have implemented tryCatch in order to make the loop keeping.

I also have added a sys.sleep() pause if an error occurs in order to wait some minutes before sending next query to the remote server (it works).

The problem is that I don't figure out how to ask the loop to redo the query that failed and lead to a tryCatch error (and to sys.sleep()).

for(i in 1:1000){
    tmp <- tryCatch({download_data(list$tool[i])},
           error = function(e) {Sys.sleep(800)})
}

Could you give me some hints?

Upvotes: 0

Views: 459

Answers (2)

AEF
AEF

Reputation: 5650

You can do something like this:

for(i in 1:1000){
   
   download_finished <- FALSE

   while(!download_finished) {

    tmp <- tryCatch({

             download_data(list$tool[i])
             download_finished <- TRUE

           },
           error = function(e) {Sys.sleep(800)})
   }
}

Upvotes: 2

Till
Till

Reputation: 6628

If you are certain that waiting for 800 seconds always fixes the issue this change should do it.

for(i in 1:1000) {
  tmp <- tryCatch({
    download_data(list$tool[i])
  },
  error = function(e) {
    Sys.sleep(800)
    download_data(list$tool[i])
  })
}

A more sophisticated approach could be, to collect the information of which request failed and then rerun the script until all requests succeed.

One way to do this is to use the possibly() function from the purrr package. It would look something like this:

todo <- rep(TRUE, length(list$tool))
res <- list()
while (any(todo)) {
  res[todo] <- map(list$tool[todo],
                   possibly(download_data, otherwise = NA))
  todo <- map_lgl(res, ~ is.na(.))
}

Upvotes: 1

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