tar_script: Write a target script file.

Description

The tar_script() function is a convenient way to create the required target script file (default: _targets.R) in the current working directory. It always overwrites the existing target script, and it requires you to be in the working directory where you intend to write the file, so be careful. See the "Target script" section for details.

Usage

tar_script(
  code = NULL,
  library_targets = TRUE,
  ask = NULL,
  script = targets::tar_config_get("script")
)

Value

NULL (invisibly).

Arguments

code: R code to write to the target script file. If NULL, an example target script file is written instead.
library_targets: logical, whether to write a library(targets) line at the top of the target script file automatically (recommended). If TRUE, you do not need to explicitly put library(targets) in code.
ask: Logical, whether to ask before writing if the target script file already exists. If NULL, defaults to Sys.getenv("TAR_ASK"). (Set to "true" or "false" with Sys.setenv()). If ask and the TAR_ASK environment variable are both indeterminate, defaults to interactive().
script: Character of length 1, where to write the target script file. Defaults to tar_config_get("script"), which in turn defaults to _targets.R.

Target script file

Every targets project requires a target script file. The target script file is usually a file called _targets.R Functions tar_make() and friends look for the target script and run it to set up the pipeline just prior to the main task. Every target script file should run the following steps in the order below:

Package: load the targets package. This step is automatically inserted at the top of the target script file produced by tar_script() if library_targets is TRUE, so you do not need to explicitly include it in code.
Globals: load custom functions and global objects into memory. Usually, this section is a bunch of calls to source() that run scripts defining user-defined functions. These functions support the R commands of the targets.
Options: call tar_option_set() to set defaults for targets-specific settings such as the names of required packages. Even if you have no specific options to set, it is still recommended to call tar_option_set() in order to register the proper environment.
Targets: define one or more target objects using tar_target().
Pipeline: call list() to aggregate the targets from (4) into a list. Every target script file must return a pipeline object, which usually means ending with a call to list(). In practice, (4) and (5) can be combined together in the same function call.

Examples

Run this code

tar_dir({ # tar_dir() runs code from a temp dir for CRAN.
tar_script() # Writes an example target script file.
# Writes a user-defined target script:
tar_script({
  library(targets)
  library(tarchetypes)
  x <- tar_target(x, 1 + 1)
  tar_option_set()
  list(x)
}, ask = FALSE)
writeLines(readLines("_targets.R"))
})

Run the code above in your browser using DataLab

Get 50% off unlimited learning