R purrr modify_tree 遞歸修改列表

modify_tree(
  x,
  ...,
  leaf = identity,
  is_node = NULL,
  pre = identity,
  post = identity
)

其他修改變體：map_depth()、modify()

x <- list(list(a = 2:1, c = list(b1 = 2), b = list(c2 = 3, c1 = 4)))
x |> str()
#> List of 1
#>  $ :List of 3
#>   ..$ a: int [1:2] 2 1
#>   ..$ c:List of 1
#>   .. ..$ b1: num 2
#>   ..$ b:List of 2
#>   .. ..$ c2: num 3
#>   .. ..$ c1: num 4

# Transform each leaf
x |> modify_tree(leaf = \(x) x + 100) |>  str()
#> List of 1
#>  $ :List of 3
#>   ..$ a: num [1:2] 102 101
#>   ..$ c:List of 1
#>   .. ..$ b1: num 102
#>   ..$ b:List of 2
#>   .. ..$ c2: num 103
#>   .. ..$ c1: num 104

# Recursively sort the nodes
sort_named <- function(x) {
  nms <- names(x)
  if (!is.null(nms)) {
    x[order(nms)]
  } else {
    x
   }
}
x |> modify_tree(post = sort_named) |> str()
#> List of 1
#>  $ :List of 3
#>   ..$ a: int [1:2] 2 1
#>   ..$ b:List of 2
#>   .. ..$ c1: num 4
#>   .. ..$ c2: num 3
#>   ..$ c:List of 1
#>   .. ..$ b1: num 2