Repeating values in a loop until the error disappears
I am currently using a for loop to geocode a large number of addresses using the Googleway package. Initially I ran into "500 Internal Server Errors" issues stopping the loop from executing. I managed to get around this with tryCatch (). However, since this tends to be a transient error, I would like the function to repeat the address that is throwing the error until it receives a result or hits some arbitrary number of attempts, say 10.
Unfortunately, I found tryCatch () and the documentation associated with it is confusing, so I don't understand how to do anything other than get it to throw an error and move on. Here is my current code:
rugeocoder.fun <- function(addr){
require(googleway)
output <- vector("list", length=length(addr))
tryCatch({
for(i in 1:length(addr)){
output[[i]] <- google_geocode(address=addr[i], key="myapikey", language="ru", simplify=T)
print(i)
}},error=function(e) output[[i]] <- "Error: reattempt")
return(output)
}
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You probably want to isolate the logic for safe invocation google_geocode()
and for address enumeration.
Here's a function that modifies other functions to call them again until they work, or they fail max_attempts
once. Functions that modify other functions are sometimes referred to as "adverbs".
safely <- function(fn, ..., max_attempts = 5) {
function(...) {
this_env <- environment()
for(i in seq_len(max_attempts)) {
ok <- tryCatch({
assign("result", fn(...), envir = this_env)
TRUE
},
error = function(e) {
FALSE
}
)
if(ok) {
return(this_env$result)
}
}
msg <- sprintf(
"%s failed after %d tries; returning NULL.",
deparse(match.call()),
max_attempts
)
warning(msg)
NULL
}
}
Try this simple function that generates a random number and throws an error if it's too small.
random <- function(lo, hi) {
y <- runif(1, lo, hi)
if(y < 0.75) {
stop("y is less than 0.75")
}
y
}
safe_random <- safely(random)
safe_random() # will sometimes work, will sometimes return NULL
safe_random(0, 10) # will usually work
In this case, you want to change the function google_geocode()
.
safe_google_geocode <- safely(google_geocode)
Then encode the addresses causing this.
geocodes <- lapply( # purrr::map() is an alternative
addresses,
safe_google_geocode,
key = "myapikey",
language = "ru",
simplify = TRUE
)
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