trigger: Customize the decision rules for rebuilding targets

Description

Use this function inside a target's command in your drake_plan() or the trigger argument to make() or drake_config(). For details, see the chapter on triggers in the user manual: https://ropenscilabs.github.io/drake-manual

Usage

trigger(command = TRUE, depend = TRUE, file = TRUE,
  condition = FALSE, change = NULL, mode = c("whitelist",
  "blacklist", "condition"))

Arguments

command

logical, whether to rebuild the target if the drake_plan() command changes.

depend

logical, whether to rebuild if a non-file dependency changes.

file

logical, whether to rebuild the target if a file_in()/file_out()/knitr_in() file changes.

condition

R code (expression or language object) that returns a logical. The target will rebuild if the code evaluates to TRUE.

change

R code (expression or language object) that returns any value. The target will rebuild if that value is different from last time or not already cached.

mode

a character scalar equal to "whitelist" (default) or "blacklist" or "condition". With the mode argument, you can choose how the condition trigger factors into the decision to build or skip the target. Here are the options.

"whitelist" (default): we rebuild the target whenever condition evaluates to TRUE. Otherwise, we defer to the other triggers. This behavior is the same as the decision rule described in the "Details" section of this help file.
"blacklist": we skip the target whenever condition evaluates to FALSE. Otherwise, we defer to the other triggers.
"condition": here, the condition trigger is the only decider, and we ignore all the other triggers. We rebuild target whenever condition evaluates to TRUE and skip it whenever condition evaluates to FALSE.

Value

A list of trigger specification details that drake processes internally when it comes time to decide whether to build the target.

Details

A target always builds if it has not been built before. Triggers allow you to customize the conditions under which a pre-existing target rebuilds. By default, the target will rebuild if and only if:

Any of command, depend, or file is TRUE, or
condition evaluates to TRUE, or
change evaluates to a value different from last time. The above steps correspond to the "whitelist" decision rule. You can select other decision rules with the mode argument described in this help file. On another note, there may be a slight efficiency loss if you set complex triggers for change and/or condition because drake needs to load any required dependencies into memory before evaluating these triggers.

Examples

Run this code

# NOT RUN {
# A trigger is just a set of decision rules
# to decide whether to build a target.
trigger()
# This trigger will build a target on Tuesdays
# and when the value of an online dataset changes.
trigger(condition = today() == "Tuesday", change = get_online_dataset())
# }
# NOT RUN {
test_with_dir("Quarantine side effects.", {
load_mtcars_example() # Get the code with drake_example("mtcars").
# You can use a global trigger argument:
# for example, to always run everything.
make(my_plan, trigger = trigger(condition = TRUE))
make(my_plan, trigger = trigger(condition = TRUE))
# You can also define specific triggers for each target.
plan <- drake_plan(
  x = sample.int(15),
  y = target(
    command = x + 1,
    trigger = trigger(depend = FALSE)
  )
)
# Now, when x changes, y will not.
make(plan)
make(plan)
plan$command[1] <- "sample.int(16)" # change x
make(plan)
})
# }