gather_by: Gather multiple groupings of targets

Description

Deprecated on 2019-05-16. Use drake_plan() transformations instead. See https://books.ropensci.org/drake/plans.html#large-plans for the details.

gather_by(
  plan,
  ...,
  prefix = "target",
  gather = "list",
  append = TRUE,
  filter = NULL,
  sep = "_"
)

A workflow plan data frame.

plan: Workflow plan data frame of prespecified targets.
...: Symbols, columns of plan to define target groupings. A gather_plan() call is applied for each grouping. Groupings with all NAs in the selector variables are ignored.
prefix: Character, prefix for naming the new targets. Suffixes are generated from the values of the columns specified in ....
gather: Function used to gather the targets. Should be one of list(...), c(...), rbind(...), or similar.
append: Logical. If TRUE, the output will include the original rows in the plan argument. If FALSE, the output will only include the new targets and commands.
filter: An expression like you would pass to dplyr::filter(). The rows for which filter evaluates to TRUE will be gathered, and the rest will be excluded from gathering. Why not just call dplyr::filter() before gather_by()? Because gather_by(append = TRUE, filter = my_column == "my_value") gathers on some targets while including all the original targets in the output. See the examples for a demonstration.
sep: Character scalar, delimiter for creating the names of new targets.

Perform several calls to gather_plan() based on groupings from columns in the plan, and then row-bind the new targets to the plan.