How to retry a statement on error?

Question

How can I simply tell R to retry a statement a few times if it errors? E.g. I was hoping to do something like:

tryCatch(dbGetQuery(...),           # Query da         


        

Answer 1

Here's a function to generate a custom condition to respond to

locked <- function(message="occurred", ...) {
    cond <- simpleCondition(message, ...)
    class(cond) <- c("locked", class(cond))
    cond
}

and a function implemented to allow (an infinite number of) restarts

f <- function() {
    cnt <- 0L
    repeat {
        again <- FALSE
        cnt <- cnt + 1L
        withRestarts({
            ## do work here, and if needed...
            signalCondition(locked())
        }, retry=function() {
            again <<- TRUE
        })
        if (!again) break
    }
    cnt
}

and the use of withCallingHandlers (to keep the context where the condition was signaled active unlike tryCatch) to handle the locked condition

withCallingHandlers({
    n_tries <- 0L
    f()
}, locked=function(e) {
    n_tries <<- n_tries + 1L
    if (n_retries < 3)
        invokeRestart("retry")
})