targets (version 0.4.1)

tar_script: Write a _targets.R script to the current working directory.

Description

The tar_script() function is a convenient way to create the required target script (_targets.R file) 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)

Arguments

code

R code to write to _targets.R. If NULL, an example target script is written instead.

library_targets

logical, whether to write a library(targets) line at the top of _targets.R automatically (recommended). If TRUE, you do not need to explicitly put library(targets) in code.

ask

Logical, whether to ask before writing if _targets.R 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().

Value

NULL (invisibly).

Target script

Every targets project requires a target script in the project root. The target script must always be named _targets.R. Functions tar_make() and friends look for _targets.R in the current working directory and use it to set up the pipeline. Every _targets.R file should run the following steps in the order below: 1. Package: load the targets package. This step is automatically inserted at the top of _targets.R files produced by tar_script() if library_targets is TRUE, so you do not need to explicitly include it in code. 1. 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. 2. 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. 3. Targets: define one or more target objects using tar_target(). 4. Pipeline: call list() to bring the targets from (3) together in a pipeline object. Every _targets.R script must return a pipeline object, which usually means ending with a call to list(). In practice, (3) and (4) can be combined together in the same function call.

See Also

Other scripts: tar_edit(), tar_github_actions(), tar_helper_raw(), tar_helper(), tar_renv()

Examples

# NOT RUN {
tar_dir({ # tar_dir() runs code from a temporary directory.
tar_script() # Writes an example target script.
# Writes a user-defined target script:
tar_script({
  x <- tar_target(x, 1 + 1)
  tar_option_set()
  list(x)
}, ask = FALSE)
writeLines(readLines("_targets.R"))
})
# }