Disregarding simple warnings/errors in tryCatch()

Question

I'm a huge fan of tryCatch(). However, until today I never really paid attention to the distinction between simple and regular warnings/errors and thus I don't really know how to handle them.

Actual question

What I'd like to know is how to tell tryCatch (see help file) that simple warnings are OK and that it should return the result of expr instead of jumping to the warning section.

Below you'll find a reproducible example

---

No tryCatch >> no warning

require("forecast")
y   <- ts(c(6178, 7084, 8162, 8462, 9644, 10466, 10748, 9963, 8194, 6848, 7027, 7269, 6775, 7819, 8371, 9069, 10248, 11030, 10882, 10333, 9109, 7685, 7602, 8350, 7829, 8829, 9948, 10638, 11253, 11424, 11391, 10665, 9396, 7775, 7933, 8186, 7444, 8484, 9864, 10252, 12282, 11637, 11577, 12417, 9637, 8094, 9280, 8334, 7899, 9994, 10078, 10801, 12950, 12222, 12246, 13281, 10366, 8730, 9614, 8639, 8772, 10894, 10455, 11179, 10588, 10794, 12770, 13812, 10857, 9290, 10925, 9491, 8919, 11607, 8852, 12537, 14759, 13667, 13731, 15110, 12185, 10645, 12161, 10840, 10436, 13589, 13402, 13103, 14933, 14147, 14057, 16234, 12389, 11595, 12772))
out <- forecast::auto.arima(x=y)
> out
Series: y 
ARIMA(4,1,1)                    

Coefficients:
         ar1      ar2     ar3      ar4      ma1
      0.6768  -0.2142  0.5025  -0.7125  -0.8277
s.e.  0.0749   0.0889  0.0874   0.0735   0.0485

sigma^2 estimated as 915556:  log likelihood=-780.33
AIC=1572.65   AICc=1573.62   BIC=1587.91

tryCatch >> simple warning

When I wrap it with tryCatch, it detects a simple warning that will cause my expr block to be "skipped" in favor of the warning section. Thus the function does not return the estimation result, but the simple warning.

mod <- tryCatch(
    out <- forecast::auto.arima(x=y),
    error=function(e) {
        print(e)
    },
    warning=function(w) {
        print(w)
    }
)

> mod 
<simpleWarning in kpss.test(x): p-value smaller than printed p-value>

Current workaround

if (any(class(mod) == "simpleWarning")) {
    mod <- forecast::auto.arima(x=y)
}

> mod
Series: y 
ARIMA(4,1,1)                    

Coefficients:
         ar1      ar2     ar3      ar4      ma1
      0.6768  -0.2142  0.5025  -0.7125  -0.8277
s.e.  0.0749   0.0889  0.0874   0.0735   0.0485

sigma^2 estimated as 915556:  log likelihood=-780.33
AIC=1572.65   AICc=1573.62   BIC=1587.91

Answer 1

I think you're looking for the difference between tryCatch, which catches a condition and continues evaluation from the environment where the tryCatch was defined, versus withCallingHandlers, which allows you to 'handle' a condition and then continue on from the location where the condition occurred. Take a look at warning (or the help page for warning, but that's less fun), especially the lines

    withRestarts({
        .Internal(.signalCondition(cond, message, call))
        .Internal(.dfltWarn(message, call))
    }, muffleWarning = function() NULL)

This says -- signal a condtion, but insert a 'restart' where the condition was signaled from. Then you'd

withCallingHandlers({
    warning("curves ahead")
    2
}, warning = function(w) {
    ## what are you going to do with the warning?
    message("warning occurred: ", conditionMessage(w))
    invokeRestart("muffleWarning")
})

Although withCallingHandlers is often used with warnings and tryCatch with errors, there is nothing to stop one from 'handling' an error or catching a warning if that is the appropriate action.