Function returns and exporting
When documenting the return value of a function, you specify what users can expect as the output of the function, whether it's data, a number, a vector of strings, or any other R result.
While the NAMESPACE file is responsible for identifying exported functions, you create this file using roxygen2 tags. By using these tags, you can easily determine whether users will have access to a function right alongside its documentation. You mark a function for exporting in the roxygen2 header. This straightforward approach ensures that you can clearly indicate which functions are available for users to work with in the documentation itself.
This exercise is part of the course
Developing R Packages
Exercise instructions
- Document the return value with the following description:
"A numeric distance value in the unit specified as `unit_to`." - Export the function.
Hands-on interactive exercise
Have a go at this exercise by completing this sample code.
#' Convert between distances
#'
#' Performs the conversion based on specified `unit_from` and `unit_to` values.
#'
#' @param dist_value A numerical distance value to be converted.
#' @param unit_from A character string of the distance unit to convert from
#' @param unit_to A character string of the distance unit to convert to
# Add returning value description and tag
___
# Export this function
___
dist_converter <- function(dist_value, unit_from, unit_to) {
if (unit_from == "feet" && unit_to == "meters") {
return(dist_value / 3.28)
} else if (unit_from == "meters" && unit_to == "feet") {
return(dist_value * 3.28)
} else if (unit_from == unit_to) {
warning("unit_from and unit_to are the same, returning dist_value")
return(dist_value)
} else {
stop("This function only supports conversions between feet and meters.")
}
}