Return nested list with nested level and value

Question

I would like to visualize some deeply nested data using networkD3. I can't figure out how to get the data into the right format before sending to radialNetwork.

Here is some sample data:

level <- c(1, 2, 3, 4, 4, 3, 4, 4, 1, 2, 3)
value <- letters[1:11]

where level indicates the level of the nest, and value is the name of the node. By using these two vectors, I need to get the data into the following format:

my_list <- list(
  name = "root",
  children = list(
    list(
      name = value[1], ## a
      children = list(list(
        name = value[2], ## b
        children = list(list(
          name = value[3], ## c
          children = list(
            list(name = value[4]), ## d
            list(name = value[5]) ## e
          )
        ),
        list(
          name = value[6], ## f
          children = list(
            list(name = value[7]), ## g
            list(name = value[8]) ## h
          )
        ))
      ))
    ),
    list(
      name = value[9], ## i
      children = list(list(
        name = value[10], ## j
        children = list(list(
          name = value[11] ## k
        ))
      ))
    )
  )
)

Here is the deparsed object:

> dput(my_list)
# structure(list(name = "root",
#                children = list(
#                  structure(list(
#                    name = "a",
#                    children = list(structure(
#                      list(name = "b",
#                           children = list(
#                             structure(list(
#                               name = "c", children = list(
#                                 structure(list(name = "d"), .Names = "name"),
#                                 structure(list(name = "e"), .Names = "name")
#                               )
#                             ), .Names = c("name",
#                                           "children")), structure(list(
#                                             name = "f", children = list(
#                                               structure(list(name = "g"), .Names = "name"),
#                                               structure(list(name = "h"), .Names = "name")
#                                             )
#                                           ), .Names = c("name",
#                                                         "children"))
#                           )), .Names = c("name", "children")
#                    ))
#                  ), .Names = c("name",
#                                "children")), structure(list(
#                                  name = "i", children = list(structure(
#                                    list(name = "j", children = list(structure(
#                                      list(name = "k"), .Names = "name"
#                                    ))), .Names = c("name",
#                                                    "children")
#                                  ))
#                                ), .Names = c("name", "children"))
#                )),
#           .Names = c("name",
#                      "children"))

Then I can pass it to the final plotting function:

library(networkD3)
radialNetwork(List = my_list)

The output will look similar to this:

---

Question: How can I create the nested list?

Note: As pointed out by @zx8754, there is already a solution in this SO post, but that requires data.frame as input. Due to the inconsistency in my level, I don't see a simple way to transform it into a data.frame.

Answer 1

Using a data.table-style merge:

library(data.table)
dt = data.table(idx=1:length(value), level, parent=value)

dt = dt[dt[, .(i=idx, level=level-1, child=parent)], on=.(level, idx < i), mult='last']

dt[is.na(parent), parent:= 'root'][, c('idx','level'):= NULL]

> dt
#     parent child
#  1:   root     a
#  2:      a     b
#  3:      b     c
#  4:      c     d
#  5:      c     e
#  6:      b     f
#  7:      f     g
#  8:      f     h
#  9:   root     i
# 10:      i     j
# 11:      j     k

Now we can use the solution from the other post:

x = maketreelist(as.data.frame(dt))

> identical(x, my_list)
# [1] TRUE