using iteration in a tar_render

[ropensci]

using iteration in a tar_render

[wlandau]

tar_render() tries to unify two opposite styles of reporting:

1. With automation: render as part of a reproducible pipeline.
2. With interactivity: render with the "Knit" button in the RStudio IDE.

If you write parameterized reports and iterate over lots of parameter values, you have abandoned (2) in favor of (1), which is why tar_render() does not try to accommodate dynamic branching. So I actually recommend:

1. Use custom functions instead of tar_render(), and
2. Reference upstream dependency targets using more conventional means instead of through tar_load() or tar_read().

Sketch:

lines <- c(
  "---",
  "title: '`r params$paramcd`'",
  "output: html_document",
  "params:",
  "  paramcd: 'TOTAL'",
  "---",
  "",
  "```{r}",
  "print(params$paramcd)",
  "print(object)",
  "```"
)

writeLines(lines, "source.Rmd")

library(targets)
tar_script({
  library(targets)
  library(tarchetypes)
  options(crayon.enabled = FALSE)
  render_output <- function(source, pars, ...) {
    output_file <- paste0(pars$paramcd, ".html")
    rmarkdown::render(
      source,
      output_file = output_file,
      params = pars,
      envir = parent.frame(), # Find targets in the environment like `object`.
      quiet = TRUE
    )
    output_file
  }
  tar_pipeline(
    tar_target(pars, data.frame(paramcd = c("param1", "param2"))),
    tar_target(object, 123),
    tar_target(source, "source.Rmd", format = "file"),
    tar_target(
      output,
      render_output(
        source = source, # Mention the Rmd source file by target name so the graph is connected.
        pars = pars,
        object = object # Mention any dependency targets by name.
      ),
      pattern = map(pars), # Dynamic branching over R Markdown parameters.
      format = "file"
    )
  )
})

tar_make()
#> ● run target object
#> ● run target pars
#> ● run target source
#> ● run branch output_36be00ef
#> ● run branch output_788b11ba

webshot::webshot("param2.html")

^{Created on 2020-12-12 by the reprex package (v0.3.0)}

[yonicd]

As always thank you for the great help!

Using targets has been a great experience and has made my workflows much more reliable reducing turnaround time for audibles from stakeholders.

[yonicd]

This also solves my other question about how to render xaringan slides in targets. Ty