pattern and map using a list variable

[franzbischoff]

My problem here is the following:

I create a list with idxs for training and test set:

  tar_target(
    idxs,
    make_idxs_split(length(file_paths), 0.75, seed = tar_seed())
  )

idxs has idxs$training and idxs$test.

The following is not working:

  tar_target(training_set,
    read_ecg(file_paths[idxs$training]),
    pattern = map(idxs$training), // or idxs[["training"]] or idxs["training"]
    format = "rds",
    resources = list(compress = "xz")
  )

it fails with Error: invalid pattern: map(idxs$training)

Digging, I see that the function settings_validate_pattern() in class_settings.R is where it stops. This because the symbols $ or [[ or [ are not recognized.

I know that the members of a dynamic list cannot be validated beforehand. So this is a bug, or is there a proper way to do this?

Thank you

[wlandau]

map() and other patterns only accept target names. so you would be able to supply map(training_ids) if training_ids were its own target.

# _targets.R
library(targets)
library(stantargets)
list(
  tar_target(idxs, make_idxs_split(length(file_paths), 0.75, seed = tar_seed())),
  tar_target(id_train, idxs$training),
  tar_target(
    training_set,
    read_ecg(file_paths[id_train]),
    pattern = map(id_train)
  )
)

If you think those input files are likely to change, consider tracking them so the relevant targets rerun when changes happen. This can be tricky with dynamic branching, but tarchetypes::tar_files_input() could help.