R 递归和函数范围变量的深度赋值

当

var这不是递归问题时，为什么深度赋值从递归函数起作用<代码>漫游流

是使用全局变量在结构上定义的。清理您的工作区并运行

get_edges

，您将看到错误。是的，完全正确。谢谢。这不是递归问题<代码>漫游流是使用全局变量在结构上定义的。清理您的工作区并运行

get_edges

，您将看到错误。是的，完全正确。谢谢

x = structure(list(flow = list(structure(list(type = "Block", id = "a"), .Names = c("type",  "id")), structure(list(type = "Branch", flow = list(structure(list( type = "Block", id = "b"), .Names = c("type", "id")), structure(list( type = "Block", id = "c"), .Names = c("type", "id")))), .Names = c("type",  "flow")))), .Names = "flow")
str(x)
# List of 1
#  $ flow:List of 2
#   ..$ :List of 2
#   .. ..$ type: chr "Block"
#   .. ..$ id  : chr "a"
#   ..$ :List of 2
#   .. ..$ type: chr "Branch"
#   .. ..$ flow:List of 2
#   .. .. ..$ :List of 2
#   .. .. .. ..$ type: chr "Block"
#   .. .. .. ..$ id  : chr "b"
#   .. .. ..$ :List of 2
#   .. .. .. ..$ type: chr "Block"
#   .. .. .. ..$ id  : chr "c"

# a global container
edges = matrix(NA, ncol = 4, nrow = 4,
  dimnames = list(c(), c("parent_id", "child_id", "child_type", "block_id")))

i = 1
uid = 0
walk_flow = function(parent) {
  parent_id = uid
  for (child in parent) {
    uid <<- uid + 1
    edges[i, c("parent_id", "child_id")] <<- c(parent_id, uid)
    edges[i, "child_type"] <<- child$type
    if (child$type == "Block") {
      edges[i, "block_id"] <<- child$id
    } else if (child$type == "Branch") {
      i <<- i + 1
      edges[i, "parent_id"] <<- uid
      walk_flow(child$flow)
      next
    }
    i <<- i + 1
  }
}
walk_flow(x$flow)
edges
#      parent_id child_id child_type block_id
# [1,] "0"       "1"      "Block"    "a"     
# [2,] "0"       "2"      "Branch"   NA      
# [3,] "2"       "3"      "Block"    "b"     
# [4,] "2"       "4"      "Block"    "c"     

get_edges = function(x) {
  edges = matrix(NA, ncol = 4, nrow = 4,
    dimnames = list(c(), c("parent_id", "child_id", "child_type", "block_id")))
  i = 1
  uid = 0
  walk_flow(x$flow)
  return(edges)
}
get_edges(x)
# Error in `[<-`(`*tmp*`, i, c("parent_id", "child_id"), value = c(5, 6)) : 
#   subscript out of bounds