Unpacks or binds values into the calling environment. Uses bquote escaping.
NULL is a special case that is unpacked to all targets. NA targets are skipped.
All non-NA target names must be unique.
# S3 method for Unpacker [(wrapr_private_self, ...) <- value
| wrapr_private_self | object implementing the feature, wrapr::unpack |
|---|---|
| ... | names of to unpack to (can be escaped with bquote |
| value | list to unpack into values, must have a number of entries equal to number of |
wrapr_private_self
Note: when using []<- notation, a reference to the unpacker object is written into the unpacking environment as a side-effect
of the implied array assignment. := assigment does not have this side-effect.
Array-assign form can not use the names: ., wrapr_private_self, value, or the name of the unpacker itself.
For more details please see here https://win-vector.com/2020/01/20/unpack-your-values-in-r/.
Related work includes Python tuple unpacking, zeallot's arrow, and vadr::bind.
# named unpacking # looks like assignment: DESTINATION = NAME_VALUE_USING d <- data.frame(x = 1:2, g=c('test', 'train'), stringsAsFactors = FALSE) to[train_set = train, test_set = test] := split(d, d$g) # train_set and test_set now correctly split print(train_set)#> x g #> 2 2 train#> x g #> 1 1 testrm(list = c('train_set', 'test_set')) # named unpacking NEWNAME = OLDNAME implicit form # values are matched by name, not index to[train, test] := split(d, d$g) print(train)#> x g #> 2 2 train#> x g #> 1 1 testrm(list = c('train', 'test')) # bquote example train_col_name <- 'train' test_col_name <- 'test' to[train = .(train_col_name), test = .(test_col_name)] := split(d, d$g) print(train)#> x g #> 2 2 train#> x g #> 1 1 test