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Showing content from https://winvector.github.io/wrapr/reference/unpack.html below:

Unpack or bind values by names into the calling environment. — unpack • wrapr

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.

unpack(wrapr_private_value, ...)

list of values to copy

argument names to write to

value passed in (invisible)

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 unpack. Function form can not use the names: . or wrapr_private_value. 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.

pack

# named unpacking
# looks like assignment: DESTINATION = NAME_VALUE_USING
d <- data.frame(
x 
= 1:2
, g
=c('test'
, 
'train')
, stringsAsFactors 
= FALSE)
unpack[
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 test
rm(
list 
= c('train_set'
, 
'test_set'))

# named unpacking NEWNAME = OLDNAME implicit form
# values are matched by name, not index
unpack[train
, 
test] := split(d
, 
d$g)
print(train)
#>   x     g
#> 2 2 train
#>   x    g
#> 1 1 test
rm(
list 
= c('train'
, 
'test'))

# function version
unpack(split(d
, 
d$g)
, 
train
, 
test)
print(train)
#>   x     g
#> 2 2 train
#>   x    g
#> 1 1 test
rm(
list 
= c('train'
, 
'test'))

# pipe version
split(d
, 
d$g) %.>% unpack(.
, 
train
, 
test)
print(train)
#>   x     g
#> 2 2 train
#>   x    g
#> 1 1 test
rm(
list 
= c('train'
, 
'test'))
# Note: above is wrapr dot-pipe, piping does not currently work with
# magrittr pipe due to magrittr's introduction of temporary
# intermediate environments during evaluation.

# bquote example
train_col_name <- 'train'
test_col_name <- 'test'
unpack(split(d
, 
d$g)
, train 
= .(train_col_name)
, test 
= .(test_col_name))
print(train)
#>   x     g
#> 2 2 train
#>   x    g
#> 1 1 test
rm(
list 
= c('train'
, 
'test'))

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