array_branch() and array_tree() enable arrays to be
used with purrr's functionals by turning them into lists. The
details of the coercion are controlled by the margin
argument. array_tree() creates an hierarchical list (a tree)
that has as many levels as dimensions specified in margin,
while array_branch() creates a flat list (by analogy, a
branch) along all mentioned dimensions.
array_branch(array, margin = NULL) array_tree(array, margin = NULL)
| array | An array to coerce into a list. |
|---|---|
| margin | A numeric vector indicating the positions of the
indices to be to be enlisted. If |
When no margin is specified, all dimensions are used by
default. When margin is a numeric vector of length zero, the
whole array is wrapped in a list.
# We create an array with 3 dimensions x <- array(1:12, c(2, 2, 3)) # A full margin for such an array would be the vector 1:3. This is # the default if you don't specify a margin # Creating a branch along the full margin is equivalent to # as.list(array) and produces a list of size length(x): array_branch(x) %>% str()#> List of 12 #> $ : int 1 #> $ : int 2 #> $ : int 3 #> $ : int 4 #> $ : int 5 #> $ : int 6 #> $ : int 7 #> $ : int 8 #> $ : int 9 #> $ : int 10 #> $ : int 11 #> $ : int 12# A branch along the first dimension yields a list of length 2 # with each element containing a 2x3 array: array_branch(x, 1) %>% str()#> List of 2 #> $ : int [1:2, 1:3] 1 3 5 7 9 11 #> $ : int [1:2, 1:3] 2 4 6 8 10 12# A branch along the first and third dimensions yields a list of # length 2x3 whose elements contain a vector of length 2: array_branch(x, c(1, 3)) %>% str()#> List of 6 #> $ : int [1:2] 1 3 #> $ : int [1:2] 2 4 #> $ : int [1:2] 5 7 #> $ : int [1:2] 6 8 #> $ : int [1:2] 9 11 #> $ : int [1:2] 10 12#> List of 2 #> $ :List of 2 #> ..$ :List of 3 #> .. ..$ : int 1 #> .. ..$ : int 5 #> .. ..$ : int 9 #> ..$ :List of 3 #> .. ..$ : int 3 #> .. ..$ : int 7 #> .. ..$ : int 11 #> $ :List of 2 #> ..$ :List of 3 #> .. ..$ : int 2 #> .. ..$ : int 6 #> .. ..$ : int 10 #> ..$ :List of 3 #> .. ..$ : int 4 #> .. ..$ : int 8 #> .. ..$ : int 12# The ordering and the depth of the tree are controlled by the # margin argument: array_tree(x, c(3, 1)) %>% str()#> List of 3 #> $ :List of 2 #> ..$ : int [1:2] 1 3 #> ..$ : int [1:2] 2 4 #> $ :List of 2 #> ..$ : int [1:2] 5 7 #> ..$ : int [1:2] 6 8 #> $ :List of 2 #> ..$ : int [1:2] 9 11 #> ..$ : int [1:2] 10 12