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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)
An array to coerce into a list.
A numeric vector indicating the positions of the
indices to be to be enlisted. If NULL, a full margin is
used. If numeric(0), the array as a whole is wrapped in a
list.
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()
# A branch along the first dimension yields a list of length 2
# with each element containing a 2x3 array:
array_branch(x, 1) %>% str()
# 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()
# Creating a tree from the full margin creates a list of lists of
# lists:
array_tree(x) %>% str()
# The ordering and the depth of the tree are controlled by the
# margin argument:
array_tree(x, c(3, 1)) %>% str()
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