Represent a hierarchical data.frame as a nested list - regex

Question

How to nicely convert a data.frame with hierarchical information to a JSON (or nested list)?
Let's say we have the following data.frame:
df <- data.frame(
id = c('1', '1.1', '1.1.1', '1.2'),
value = c(10, 5, 5, 5))
# id value
# 1 10
# 1.1 5
# 1.1.1 5
# 1.2 5
Then I would like to end up with the following JSON:
{
"id": "1",
"value": 10,
"children": [
{
"id": "1.1",
"value": 5,
"children": [
{
"id": "1.1.1",
"value": 5
}
]
},
{
"id": "1.2",
"value": 5
}
]
}
Where id defines the hierarchical structure, and . is a delimiter.
My intention is to easily be able to convert data from R to hierarchical D3 visualisations (e.g. Partition Layout or Zoomable Treemaps). It would also be nice if it is possible to add more "value"-columns; e.g value, size, weight, etc.
Thank you!
EDIT: I reverted to the original question, so it is easier to follow all the answers (sorry for all the editing).

Answer 1

I tend to have RJSONIO installed which does this:
R> df <- data.frame(id = c('1', '1.1', '1.1.1', '1.2'), value = c(10, 5, 5, 5))
R> RJSONIO::toJSON(df)
[1] "{\n \"id\": [ \"1\", \"1.1\", \"1.1.1\", \"1.2\" ],\n\"value\": [ 10, 5, 5, 5 ] \n}"
R> cat(RJSONIO::toJSON(df), "\n")
{
"id": [ "1", "1.1", "1.1.1", "1.2" ],
"value": [ 10, 5, 5, 5 ]
}
R>
That is not your desired output but the desired nesting / hierarchy was not present in the data.frame. I think if you nest a data.frame inside a list you will get there.
Edit: For your revised question, here is the R output of reading you spec'ed JSON back in:
R> RJSONIO::fromJSON("/tmp/foo.json")
$id
[1] "1"
$value
[1] 10
$children
$children[[1]]
$children[[1]]$id
[1] "1.1"
$children[[1]]$value
[1] 5
$children[[1]]$children
$children[[1]]$children[[1]]
$children[[1]]$children[[1]]$id
[1] "1.1.1"
$children[[1]]$children[[1]]$value
[1] 5
$children[[2]]
$children[[2]]$id
[1] "1.2"
$children[[2]]$value
[1] 5
R>

Answer 2

A possible solution.
First I define the following functions:
# Function to get the number hierarchical dimensions (occurences of "." + 1)
ch_dim <- function(x, delimiter = ".") {
x <- as.character(x)
chr.count <- function(x) length(which(unlist(strsplit(x, NULL)) == delimiter))
if (length(x) > 1) {
sapply(x, chr.count) + 1
} else {
chr.count(x) + 1
}
}
# Function to convert a hierarchical data.frame to a nested list
lst_fun <- function(ch, id_col = "id", num = min(d), stp = max(d)) {
# Convert data.frame to character
ch <- data.frame(lapply(ch, as.character), stringsAsFactors=FALSE)
# Get number of hierarchical dimensions
d <- ch_dim(ch[[id_col]])
# Convert to list
lapply(ch[d == num,][[id_col]], function(x) {
tt <- ch[grepl(sprintf("^%s.", x), ch[[id_col]]),]
current <- ch[ch[[id_col]] == x,]
if (stp != num && nrow(tt) > 0) {
c(current, list(children = lst_fun(tt, id_col, num + 1, stp)))
} else { current }
})
}
then convert the data.frame to a list:
lst <- lst_fun(df, "id")
and finally, the JSON:
s <- RJSONIO::toJSON(lst)