Post about ellipsis

[Bisaloo]

• present base R features to play with ...: ...names(), ...elt(n), ...length(), etc.
• when to use ...?
  • pass arguments to a function chosen by the user (e.g. apply())
  • S3 methods
  • forward compatibility
• base R function chkDots()
• explain how to pass a default value to an argument in ...

f <- function(x, ...) {
  
  xargs <- list(...)
  
  if (is.null(xargs$na.rm))
    xargs$na.rm <- TRUE
  
  xargs$x <- x
  
  do.call(quantile, xargs)
  
}

f(1:10)
#>    0%   25%   50%   75%  100% 
#>  1.00  3.25  5.50  7.75 10.00

f(c(1:10, NA))
#>    0%   25%   50%   75%  100% 
#>  1.00  3.25  5.50  7.75 10.00

f(c(1:10, NA), na.rm = FALSE)
#> Error in quantile.default(na.rm = FALSE, x = c(1L, 2L, 3L, 4L, 5L, 6L, : missing values and NaN's not allowed if 'na.rm' is FALSE

^{Created on 2022-03-11 by the reprex package (v2.0.1.9000)}

• explanation of the differences between the various approaches presented in this tweet? evaluated vs non-evaluated
• https://ellipsis.r-lib.org/

Bonus: Options for clickbait title

"Everything you've always wanted to know about ..."

[maelle]

I like the idea and the title 😂

Another use case is to have some sort of DSL. E.g. in glitter we use .... We then handle the passed things with rlang::enquos().

[maelle]

https://design.tidyverse.org/dots-after-required.html

[maelle]

https://rlang.r-lib.org/reference/index.html#check-dots