Build Tree

Captures the nesting structure of an object as an opaque RTree. Each leaf in the input corresponds to its position in the flat list produced by flatten(). The resulting tree can be passed to unflatten() to reconstruct the original structure from a flat list.

NULL is an empty node: it holds no leaf and contributes nothing to the flat list, but is preserved in the tree (so list(x, NULL) and list(NULL, x) have distinct trees).

The RTree and its operations are pjrt's R analog of JAX's pytree, which is where the idea comes from.

Usage

build_tree(x)

Arguments

x

(any)
Object whose structure to capture. Bare lists are recursed into; everything else is a leaf.

Value

A RTree.

See also

flatten(), unflatten(), tree_size()

Examples

x <- list(a = 1, b = list(c = 2, d = 3))
tree <- build_tree(x)
tree_size(tree)
#> [1] 3

unflatten(tree, flatten(x))
#> $a
#> [1] 1
#> 
#> $b
#> $b$c
#> [1] 2
#> 
#> $b$d
#> [1] 3
#> 
#>