Creating a target for a plot and a file

[Shians]

Help

• I understand and agree to https://books.ropensci.org/targets/help.html.

Description

I find myself using the following pattern a lot

list(
    tar_target(plot, plot_fn()),
    tar_files(plot_files, save_fn(plot, "plot.png")
)

The expression capturing in the source code of this package are beyond my understanding, so I was wondering whether there's an existing function available or how an implementation would look like such that I can instead use

list(
    tar_plot(plot, plot_fn, save_fn, path = "plot.png")
)

Ideally it would track *_plot and *_file objects.

[wlandau]

I will have to think about officially supporting this in tarchetypes. But for now, you can use your own target factory.

# _targets.R file
library(targets)
library(tarchetypes)

tar_plot <- function(name, fun_plot, fun_save, path) {
  name <- substitute(name)
  prefix <- as.character(name)
  name_plot <- paste0(name, "_plot")
  name_file <- paste0(name, "_file")
  list(
    targets::tar_target_raw(
      name = name_plot,
      command = substitute(
        fun(),
        env = list(fun = substitute(fun_plot))
      )
    ),
    targets::tar_target_raw(
      name = name_file,
      command = substitute(
        fun(plot, path),
        env = list(
          fun = substitute(fun_save),
          plot = as.symbol(name_plot),
          path = path
        )
      )
    )
  )
}

tar_plot(my_name, my_plot, my_save, "path.png")

# R console
tar_manifest()
#> # A tibble: 2 × 2
#>   name         command                              
#>   <chr>        <chr>                                
#> 1 my_name_plot "my_plot()"                          
#> 2 my_name_file "my_save(my_name_plot, \"path.png\")"

[Shians]

Thank you very much for this! If it doesn't already exist, it would be very useful to document the process of creating a custom complex targets such as these, in particular I think the proper usage of substitute() is difficult to understand.

[wlandau]

I wrote about this at https://wlandau.github.io/targetopia/contributing.html.