How to use dynamic files to update drake directory

Question

I want to make sure that my drake plan will update when I add new .csv files to a directory. I looked into the new dynamic files, but couldn't get this to work (see reprex).

library(drake)
library(purrr)
library(readr)
fs::dir_create("folder")
file.create("folder/file1.csv")
#> [1] TRUE

# Single dynamic file
plan_base <- drake_plan(
  upstream = target(
    list.files("folder", full.names = TRUE),
  format = "file"
),
downstream = map_dfr(upstream, read_csv)
)

make(plan_base)
#> ▶ target upstream
#> ▶ target downstream
#> Warning: `data_frame()` is deprecated as of tibble 1.1.0.
#> Please use `tibble()` instead.
#> This warning is displayed once every 8 hours.
#> Call `lifecycle::last_warnings()` to see where this warning was generated.

# Updates when changing the file
write_csv(mtcars, "folder/file1.csv")

plan_update <- drake_plan(
  upstream = target(
    list.files("folder", full.names = TRUE),
    format = "file"
  ),
  downstream = map_dfr(upstream, read_csv)
)

make(plan_update)
#> ▶ target upstream
#> ▶ target downstream
#> Parsed with column specification:
#> cols(
#>   mpg = col_double(),
#>   cyl = col_double(),
#>   disp = col_double(),
#>   hp = col_double(),
#>   drat = col_double(),
#>   wt = col_double(),
#>   qsec = col_double(),
#>   vs = col_double(),
#>   am = col_double(),
#>   gear = col_double(),
#>   carb = col_double()
#> )

# Doesn't update when adding file to directory
file.create("folder/file2.csv")
#> [1] TRUE

plan_no_update <- drake_plan(
  upstream = target(
    list.files("folder", full.names = TRUE),
    format = "file"
  ),
  downstream = map_dfr(upstream, read_csv)
)

make(plan_no_update)
#> ✓ All targets are already up to date.

^{Created on 2020-07-17 by the reprex package (v0.3.0)}

devtools::session_info()
#> ─ Session info ───────────────────────────────────────────────────────────────
#>  setting  value                       
#>  version  R version 4.0.1 (2020-06-06)
#>  os       macOS Mojave 10.14.6        
#>  system   x86_64, darwin17.0          
#>  ui       X11                         
#>  language (EN)                        
#>  collate  en_AU.UTF-8                 
#>  ctype    en_AU.UTF-8                 
#>  tz       Australia/Sydney            
#>  date     2020-07-17                  
#> 
#> ─ Packages ───────────────────────────────────────────────────────────────────
#>  package     * version date       lib source        
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Answer 1

Directories work as dynamic files too, so there is actually no need to list the specific contents if you track an entire directory. Try this:

plan <- drake_plan(
  upstream = target("folder", format = "file"),
  downstream = map_dfr(upstream, read_csv)
)

There are alternatives, but they are more complicated. One is to set the condition trigger to TRUE so the target always runs, but this is not as efficient because it will recompute hashes even if the files are large.

plan_no_update <- drake_plan(
  upstream = target(
    list.files("folder", full.names = TRUE),
    format = "file",
    trigger = trigger(condition = TRUE)
  ),
  downstream = map_dfr(upstream, read_csv)
)

Another alternative is to define the files as global objects outside the plan first so they always refresh before you run make().

plan <- drake_plan(
  upstream = target(files, format = "file"),
  downstream = map_dfr(upstream, read_csv)
)
files <- list.files("folder", full.names = TRUE)
make(plan)