Coerce arguments to simplest type

user_2270475 0
Viewed 78

When dealing with user input using packages shiny or plumber one often needs to convert character arguments to numeric or logical.

I would like to do it automatically, what's an efficient way to do it ?

expected (this or similar) : 

convert_args <- ...

fun <- function(a, b, c, d){
  convert_args()
  dplyr::lst(a, b, c , d)
}

fun("na","true","1","foo")
#> $a
#> [1] NA
#> 
#> $b
#> [1] TRUE
#> 
#> $c
#> [1] 1
#> 
#> $d
#> [1] "foo"
plumber shiny r type-conversion
2 Answers

One option is to use readr::parse_guess which as the name suggests tries to guess the type of the character vector. 

convert_args <- function(x) {
  lapply(x, readr::parse_guess)  
}

convert_args(c("NA","true","1","foo"))
#[[1]]
#[1] NA

#[[2]]
#[1] TRUE

#[[3]]
#[1] 1

#[[4]]
#[1] "foo"

This doesn't directly work when we have "na" 

readr::parse_guess("na")
#[1] "na"

but as @Moody_Mudskipper mentions it can be resolved specifying na argument in parse_guess

readr::parse_guess("na", c("na", "NA"))
#[1] NA
user_39629140

I built a wrapper around readr::parse_guess thanks to @Ronak's solution to get exactly the expected output.

I also added an option to evaluate the unconverted character input as it's a common task as well.


convert_args <- function(na = c("", "NA"), locale = readr::default_locale(),
                         trim_ws = TRUE, guess_integer = FALSE, eval = FALSE){
  if(!requireNamespace("readr")) 
    stop("convert_args() requires package readr to be installed")
  args <- as.list(eval.parent(quote(match.call())))[-1]
  args <- lapply(args, readr::parse_guess, na, locale, trim_ws, guess_integer)
  if (eval){
    args <- lapply(args, function(arg) {
      if(is.character(arg))
        eval(parse(text = arg, parent.frame(2)))
      else
        arg
    })
  }
  list2env(args, envir = parent.frame())
  invisible(NULL)
}

fun <- function(a, b, c, d){
  convert_args()
  dplyr::lst(a, b, c , d)
}


fun("NA","true","1","head(cars,2)")
#> Loading required namespace: readr
#> $a
#> [1] NA
#> 
#> $b
#> [1] TRUE
#> 
#> $c
#> [1] 1
#> 
#> $d
#> [1] "head(cars,2)"

fun2 <- function(a, b, c, d){
  convert_args(eval = TRUE, na = c("na","NA"))
  dplyr::lst(a, b, c , d)
}

fun2("na","true","1","head(cars,2)")
#> $a
#> [1] NA
#> 
#> $b
#> [1] TRUE
#> 
#> $c
#> [1] 1
#> 
#> $d
#>   speed dist
#> 1     4    2
#> 2     4   10

Created on 2019-06-21 by the reprex package (v0.3.0)

user_22704750
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