Utility for clean()ing everything but the contents of a plan

[kendonB]

Prework

• Read and abide by drake's code of conduct.
• Search for duplicates among the existing issues, both open and closed.

Proposal

Why dynamic branching, it's now a bit of work to subset the cached() targets to only those not in a plan, given many of the targets in cached() have a hash suffix (i.e. they're expanded) and the plan$target names have the unexpanded target name.

It would be neat to be able to run something like clean(plan_to_exclude = myplan) and the system would only clean those targets that wouldn't get built from myplan.

[wlandau]

Good idea. Added cached_unplanned() and cached_planned() in 99a2926.

library(drake)
plan <- drake_plan(w = 1)
make(plan)
#> target w
plan <- drake_plan(
  x = seq_len(2),
  y = target(x, dynamic = map(x))
)
make(plan)
#> target x
#> dynamic y
#> subtarget y_0b3474bd
#> subtarget y_b2a5c9b8
#> aggregate y
cached()
#> [1] "w"          "x"          "y"          "y_0b3474bd" "y_b2a5c9b8"
clean(list = cached_unplanned(plan))
cached()
#> [1] "x"          "y"          "y_0b3474bd" "y_b2a5c9b8"

^{Created on 2019-12-12 by the reprex package (v0.3.0)}