Recursively flattens a list. Unlike the similar unlist(), it
always returns a list, i.e. wraps
xin a list if necessary, and will never remove the last list level. Thus it is type-safe.won't treat any of the list leafs specially (like
unlist()does with factors). Thus leaf values will never be modified.removes list names.
unlist()concatenates nested names (separated by a dot).
Arguments
- x
An R object.
- keep_attrs
Keep attributes (and thereby retain list structure of custom objects). A logical scalar.
- attrs_to_drop
Attribute names which should never be kept. Only relevant if
keep_attrs = TRUE. A character vector.
Value
A list.
Examples
library(magrittr)
nested_list <- list(1:3, list("foo", list("bar"))) %T>% str()
#> List of 2
#> $ : int [1:3] 1 2 3
#> $ :List of 2
#> ..$ : chr "foo"
#> ..$ :List of 1
#> .. ..$ : chr "bar"
# unlike `unlist()` which also removes the last list tier in many cases...
unlist("foobar")
#> [1] "foobar"
unlist(nested_list) |> str()
#> chr [1:5] "1" "2" "3" "foo" "bar"
# ...this function always returns an (unnested) list
pal::as_flat_list("foobar") |> str()
#> List of 1
#> $ : chr "foobar"
pal::as_flat_list(nested_list) |> str()
#> List of 3
#> $ : int [1:3] 1 2 3
#> $ : chr "foo"
#> $ : chr "bar"
nested_list <- list(list(factor("a"), factor("b")), factor("c")) %T>% str()
#> List of 2
#> $ :List of 2
#> ..$ : Factor w/ 1 level "a": 1
#> ..$ : Factor w/ 1 level "b": 1
#> $ : Factor w/ 1 level "c": 1
# unlike `unlist()` which combines factors...
unlist(nested_list) |> str()
#> Factor w/ 3 levels "a","b","c": 1 2 3
# ...this function does not modify the list elements
pal::as_flat_list(nested_list) |> str()
#> List of 3
#> $ : Factor w/ 1 level "a": 1
#> $ : Factor w/ 1 level "b": 1
#> $ : Factor w/ 1 level "c": 1
nested_list <-
list(c(list(1L), list(tibble::tibble(a = list(1.1, "2")))),
list(tibble::as_tibble(mtcars[1:2, ]))) %T>%
str()
#> List of 2
#> $ :List of 2
#> ..$ : int 1
#> ..$ : tibble [2 × 1] (S3: tbl_df/tbl/data.frame)
#> .. ..$ a:List of 2
#> .. .. ..$ : num 1.1
#> .. .. ..$ : chr "2"
#> $ :List of 1
#> ..$ : tibble [2 × 11] (S3: tbl_df/tbl/data.frame)
#> .. ..$ mpg : num [1:2] 21 21
#> .. ..$ cyl : num [1:2] 6 6
#> .. ..$ disp: num [1:2] 160 160
#> .. ..$ hp : num [1:2] 110 110
#> .. ..$ drat: num [1:2] 3.9 3.9
#> .. ..$ wt : num [1:2] 2.62 2.88
#> .. ..$ qsec: num [1:2] 16.5 17
#> .. ..$ vs : num [1:2] 0 0
#> .. ..$ am : num [1:2] 1 1
#> .. ..$ gear: num [1:2] 4 4
#> .. ..$ carb: num [1:2] 4 4
nested_list_2 <- list(1:3, xfun::strict_list(list(list("buried deep")))) %T>% str()
#> List of 2
#> $ : int [1:3] 1 2 3
#> $ :List of 1
#> ..$ :List of 1
#> .. ..$ :List of 1
#> .. .. ..$ : chr "buried deep"
#> ..- attr(*, "class")= chr "xfun_strict_list"
# by default, attributes and thus custom objects (except `xfun_strict_list`) are retained, i.e.
# not flattened...
pal::as_flat_list(nested_list) |> str()
#> List of 3
#> $ : int 1
#> $ : tibble [2 × 1] (S3: tbl_df/tbl/data.frame)
#> ..$ a:List of 2
#> .. ..$ : num 1.1
#> .. ..$ : chr "2"
#> $ : tibble [2 × 11] (S3: tbl_df/tbl/data.frame)
#> ..$ mpg : num [1:2] 21 21
#> ..$ cyl : num [1:2] 6 6
#> ..$ disp: num [1:2] 160 160
#> ..$ hp : num [1:2] 110 110
#> ..$ drat: num [1:2] 3.9 3.9
#> ..$ wt : num [1:2] 2.62 2.88
#> ..$ qsec: num [1:2] 16.5 17
#> ..$ vs : num [1:2] 0 0
#> ..$ am : num [1:2] 1 1
#> ..$ gear: num [1:2] 4 4
#> ..$ carb: num [1:2] 4 4
pal::as_flat_list(nested_list_2) |> str()
#> List of 2
#> $ : int [1:3] 1 2 3
#> $ : chr "buried deep"
# ...but you can drop them and thereby flatten custom objects if needed...
pal::as_flat_list(nested_list, keep_attrs = FALSE) |> str()
#> List of 4
#> $ : int 1
#> $ : num 1.1
#> $ : chr "2"
#> $ : tibble [2 × 11] (S3: tbl_df/tbl/data.frame)
#> ..$ mpg : num [1:2] 21 21
#> ..$ cyl : num [1:2] 6 6
#> ..$ disp: num [1:2] 160 160
#> ..$ hp : num [1:2] 110 110
#> ..$ drat: num [1:2] 3.9 3.9
#> ..$ wt : num [1:2] 2.62 2.88
#> ..$ qsec: num [1:2] 16.5 17
#> ..$ vs : num [1:2] 0 0
#> ..$ am : num [1:2] 1 1
#> ..$ gear: num [1:2] 4 4
#> ..$ carb: num [1:2] 4 4
# ...or retain `xfun_strict_list`s, too
pal::as_flat_list(nested_list_2, attrs_to_drop = NULL) |> str()
#> List of 2
#> $ : int [1:3] 1 2 3
#> $ :List of 1
#> ..$ :List of 1
#> .. ..$ :List of 1
#> .. .. ..$ : chr "buried deep"
#> ..- attr(*, "class")= chr "xfun_strict_list"