In the command of each target, wrap each mention of each dependency target in an arbitrary R expression.
Arguments
- targets
A list of target objects. The input target list can be arbitrarily nested, but it must consist entirely of target objects. In addition, the return value is a simple list where each element is a target object. All hook functions remove the nested structure of the input target list.
- hook
R code to wrap each target's command. The hook must contain the special placeholder symbol
.x
sotar_hook_inner()
knows where to insert the code to wrap mentions of dependencies. The hook code is quoted (not evaluated) so there is no need to wrap it inquote()
,expression()
, or similar.- names
Name of targets in the target list to apply the hook. Supplied with
tidyselect
helpers likestarts_with()
, as innames = starts_with("your_prefix_")
. Targets not included innames
still remain in the target list, but they are not modified because the hook does not apply to them.- names_wrap
Names of targets to wrap with the hook where they appear as dependencies in the commands of other targets. Use
tidyselect
helpers likestarts_with()
, as innames_wrap = starts_with("your_prefix_")
.- set_deps
Logical of length 1, whether to refresh the dependencies of each modified target by scanning the newly generated target commands for dependencies. If
FALSE
, then the target will keep the original set of dependencies it had before the hook.TRUE
is recommended for nearly all situations. Only useFALSE
if you have a specialized use case and you know what you are doing.
Value
A flattened list of target objects with the hooks applied. Even if the input target list had a nested structure, the return value is a simple list where each element is a target object. All hook functions remove the nested structure of the input target list.
Details
The expression you supply to hook
must contain the special placeholder symbol .x
so tar_hook_inner()
knows where to insert the original command
of the target.
Target objects
Most tarchetypes
functions are target factories,
which means they return target objects
or lists of target objects.
Target objects represent skippable steps of the analysis pipeline
as described at https://books.ropensci.org/targets/.
Please read the walkthrough at
https://books.ropensci.org/targets/walkthrough.html
to understand the role of target objects in analysis pipelines.
For developers, https://wlandau.github.io/targetopia/contributing.html#target-factories explains target factories (functions like this one which generate targets) and the design specification at https://books.ropensci.org/targets-design/ details the structure and composition of target objects.
See also
Other hooks:
tar_hook_before()
,
tar_hook_outer()
Examples
if (identical(Sys.getenv("TAR_LONG_EXAMPLES"), "true")) {
targets::tar_dir({ # tar_dir() runs code from a temporary directory.
targets::tar_script({
targets <- list(
# Nested target lists work with hooks.
list(
targets::tar_target(x1, task1()),
targets::tar_target(x2, task2(x1))
),
targets::tar_target(x3, task3(x2, x1)),
targets::tar_target(y1, task4(x3))
)
tarchetypes::tar_hook_inner(
targets = targets,
hook = fun(.x),
names = starts_with("x")
)
})
targets::tar_manifest(fields = command)
})
}