How can I set a conditional function argument value here? - r

Question

I want to automatically set the value of an argument in a function based on another argument's value.
More specifically, I want to set a timezone value (offset) to automatically adjust time values given the region.
However, my implementation doesn't seem to work (as in the offset is never applied unless I specifically pass it as an argument to the function).
Part of the function (is supposed to) set the offset value based on region's value, and also connect to the corresponding Elasticsearch server.
This is what I have:
if (region == "EU") {
offset = "+00:00:00"
# Code to connect to EU ElasticSearch server
} else if (region == "US") {
offset = "-06:00:00"
# Code to connect to US ElasticSearch server
} else {
paste0(stop("Incorrect region supplied: ", region))
}
The function:
time_function <- function(region, retailer, start_date, end_date, offset = "+00:00:00"){
# Function body
}
(Note that I have set the default value of offset to "+00", otherwise it will throw an error that the argument is missing.)
Clearly I have gone wrong somewhere because the offset is never applied unless I explicitly specify in the argument list.
This is what I want to do:
If region == "US", then set offset to "-06:00:00",
Else if region == "EU", then set offset to "+00:00:00"
Else Error message: "supply valid region"
In short, I am looking to set a conditional argument value.
How can I achieve this?

Answer 1

It turns out I made an oversight in the order of assignment implementations and have just now spotted it.
For those who might be experiencing similar problems, it might be worth highlighting where I went wrong: I set the offset value after it was used, meaning that it was used/processed (using the previous iteration's value) and then it was assigned the new value.
In short, my implementation was completely correct but the order of events was incorrect.
Therefore, make sure that you set the required values before they are processed.

Answer 2

Your code work.
> time_function <- function(region){
+ # Function body
+ if (region == "EU") {
+ offset = "+00:00:00"
+ # Code to connect to EU ElasticSearch server
+ } else if (region == "US") {
+ offset = "-06:00:00"
+ # Code to connect to US ElasticSearch server
+ } else {
+ stop(paste0("Incorrect region supplied: ", region))
+ }
+
+ return(offset)
+ }
>
> time_function("EU")
[1] "+00:00:00"
> time_function("US")
[1] "-06:00:00"
> time_function("CH")
Error in time_function("CH") : Incorrect region supplied: CH
To optimize your code, you can use the switch.
> time_function <- function(region){
+ # Function body
+ offset <- switch(region,
+ EU = "+00:00:00",
+ US = "-06:00:00",
+ stop(paste0("Incorrect region supplied: ", region)))
+
+ return(offset)
+ }
>
> time_function("EU")
[1] "+00:00:00"
> time_function("US")
[1] "-06:00:00"
> time_function("CH")
Error in time_function("CH") : Incorrect region supplied: CH
With two parameters:
> time_function <- function(region){
+ # Function body
+ list2env(switch(region,
+ EU = list(offset = "+00:00:00", con = "EU_con"),
+ US = list(offset = "+00:00:00", con = "US_con"),
+ stop(paste0("Incorrect region supplied: ", region))), envir = environment())
+
+ return(c(offset, con))
+ }
>
> time_function("EU")
[1] "+00:00:00" "EU_con"
> time_function("US")
[1] "+00:00:00" "US_con"
> time_function("CH")
Error in list2env(switch(region, EU = list(offset = "+00:00:00", con = "EU_con"), :
Incorrect region supplied: CH