targets_dynamic_branching_group_iteration.R

library(targets)
tar_dir({
  #create 10 identical CSVs as a demo
  orig <- tibble::tibble(group = c("A", "A", "A", "B", "B", "C"),
                         value = 1)
  purrr::walk(c(1:10), \(x) write_csv(orig, paste0(x, "-data.csv")))
  
  #_targets.R
  tar_script({
    library(targets)
    library(fs)
    library(readr)
    library(dplyr)
    list(
      tar_target(files, dir_ls(glob = "*.csv")),
      tar_target(
        df,
        read_csv(files), 
        pattern = map(files), #=do this for each file
        iteration = "vector" #combine into a single data frame when loaded
      ),
      tar_target(
        df_grouped, 
        df |> group_by(group) |> tar_group(),
        iteration = "group", #downstream targets should iterate over groups
        # pattern = map(files) #this errors, can't use dynamic branching
      ), 
      tar_target(
        summary_per_group,
        summarize(df_grouped, sum = sum(value)),
        pattern = map(df_grouped) #=do this for each group in df_grouped
      )
    )
  })
  tar_make()
  # tar_read(df) #a single dataframe with 60 rows (combined because iteration = "vector")
  # tar_read(df_grouped) #a single dataframe with 60 rows and a tar_group column
  tar_read(summary_per_group) #a single dataframe with 3 rows (one per tar_group) and 1 column
})

# https://gist.github.com/Aariq/b5adeb0af436c3d8a9a5f889bf69921e