Wrapping DT

wrapping-dt.R

# Simple DT wrapper
summarise <- function(data, j, by) {
  data <- data.table::as.data.table(data)
  data[
    i = ,
    j = eval(substitute(j)),
    by = eval(substitute(by))
  ]
}

# It works in simple cases, though the columns don't have good default labels:
summarise(mtcars, mean(disp), cyl)
#>    substitute       V1
#> 1:          6 183.3143
#> 2:          4 105.1364
#> 3:          8 353.1000

# The main issue is that it can't be reused in packages:
local({
  mysummary <- mean  # Simulating package function
  summarise(mtcars, mysummary(disp), cyl)
})
#> Error in mysummary(disp) : could not find function "mysummary"


# The wrapper can't be rewrapped easily:
summarise_cyl <- function(data, j) {
  summarise(data, j, by = cyl)
}
summarise_cyl(mtcars, mean(disp))
#> Error in mean(disp) : object 'disp' not found


# Needs to use eval(), bquote(), and substitute()
summarise_cyl <- function(data, j) {
  eval(bquote(summarise(data, .(substitute(j)), by = cyl)))
}

summarise_cyl(mtcars, mean(disp))
#>    substitute       V1
#> 1:          6 183.3143
#> 2:          4 105.1364
#> 3:          8 353.1000

# Can't be reused in package:
local({
  x <- 10
  summarise_cyl(mtcars, mean(disp) * x)
})
#> Error in `[.data.table`(data, i = , j = eval(substitute(j)), by = eval(substitute(by))) : 
#>   object 'x' not found