Extract Edgelist from a List

Recursively traverses a nested list structure, producing a parent-child edgelist. Each element of the list becomes a node; nested lists create deeper edges. Path-style IDs ensure unique node names even when element names repeat at different levels.

Usage

# S3 method for class 'list'
edgelist(input_object, name_root = "root", max_depth = NULL, ...)

Arguments

input_object

A list (or S3 object falling through to this method).

name_root

Character; label for the root node. Defaults to "root".

max_depth

Integer or NULL; maximum node depth to include (root is depth 0, its children are depth 1). NULL (the default) means unlimited. max_depth = 0 returns an empty edgelist (root only).

...

Additional arguments (currently unused).

Value

A data.frame with columns from, to, and depth (integer depth of the child node, root children are depth 1). An empty list returns a zero-row data.frame with the same columns.

Details

When called on an S3 object that has no dedicated edgelist method (e.g. an lm object), the object is treated as a plain list and a diagnostic message is emitted. To force structural decomposition of an object that has its own method (e.g. a tree), use edgelist(unclass(x)).

Examples

edgelist(list(a = 1, b = list(c = 2, d = 3)))
#>     from       to depth
#> 1   root   root/a     1
#> 2   root   root/b     1
#> 3 root/b root/b/c     2
#> 4 root/b root/b/d     2

# Unnamed elements use positional indices
edgelist(list(1, 2, list(3, 4)))
#>         from               to depth
#> 1       root       root/[[1]]     1
#> 2       root       root/[[2]]     1
#> 3       root       root/[[3]]     1
#> 4 root/[[3]] root/[[3]]/[[1]]     2
#> 5 root/[[3]] root/[[3]]/[[2]]     2

# Limit depth (root = 0, children = 1, ...)
edgelist(list(a = list(b = list(c = 1))), max_depth = 2)
#>     from       to depth
#> 1   root   root/a     1
#> 2 root/a root/a/b     2