If error, next iteration in a for loop in R - r

Question

I'm looking for a simple way to move on to the next iteration in a for loop in R if the operation inside the for loop errors.
I've recreated a simple case below:
for(i in c(1, 3)) {
test <- try(i+1, silent=TRUE)
calc <- if(class(test) %in% 'try-error') {next} else {i+1}
print(calc)
}
This correctly gives me the following calc values.
[1] 2
[1] 4
However once I change the vector in i to include a non-numeric value:
for(i in c(1, "a", 3)) {
test <- try(i+1, silent=TRUE)
calc <- if(class(test) %in% 'try-error') {next} else {i+1}
print(calc)
}
This for loop doesn't work. I was hoping for the same calc values as above with the vector excluding the non-numeric value in i.
I tried using tryCatch as the following:
for(i in c(1, "a", 3)) {
calc <- tryCatch({i+1}, error = function(e) {next})
print(calc)
}
However, I get the following error:
Error in value[[3L]](cond) : no loop for break/next, jumping to top level
Could someone please help me understand how I could achieve this using a for loop in R?

Answer 1

As Dason noted, an atomic vector really is not the best way of storing mixed data types. Lists are for that. Consider the following:
l = list(1, "sunflower", 3)
for(i in seq_along(l)) {
this.e = l[[i]]
test <- try(this.e + 1, silent=TRUE)
calc <- if(class(test) %in% 'try-error') {next} else {this.e + 1}
print(calc)
}
[1] 2
[1] 4
In other words, your former loop "worked". It just always failed and went to next iteration.

Answer 2

Here is a solution using the "purr" package that might be helpful.
It goes through your list or vector and returns the elements that will cause errors
#Wrap the function you want to use in the adverb "safely"
safetest <- safely(function(x){ifelse(is.na(as.numeric(x)),
x+1,
as.numeric(x)+1)})
myvect<-c(1,"crumbs",3) #change to list if you want a list
#Use the safe version to find where the errors occur
check <- myvect %>%
map(safetest) %>%
transpose %>% .$result %>%
map_lgl(is_null)
myvect[check]
#This returns the results that did not through an error
#first remove NULL elements then flatten to double.
#The two flatten expresiion can be replaced by a single unlist
myvect %>%
map(safetest) %>%
transpose %>% .$result %>%
flatten()%>%flatten_dbl()
see https://blog.rstudio.org/2016/01/06/purrr-0-2-0/ for the original example.