Nested list assignment R - r

Question

I have a list of the following type
categories = list(
c("Women","Clothing", "Jeans"),
c("Women","Clothing", "Sweaters"),
c("Men","Accessories", "Belts"),
c("Women", "Accessories", "Jewelry" ))
I want to parse this list and create a list of lists to export in JSON and it should have the following structure:
Women={
Clothing= {
Jeans{},
Sweaters{}
},
accesories={
Jewleery{}
}
},
Men ={
Accessires={
Belts={}
}
So it should go over each element which is a char vector contained in the list and check if there is such element in the final list, if there isn't it should append it. It should append the element at the proper level. For example if Clothing is second element to Woman, it should append to the Women list of the final list. Or if Sweaters is thrid element to Women.Clothing it should apppend Clothing list of the Women list of the final list.
If the element exists at the given level already it should not append, instead it should go to next element in the char vector.
In the char vectors of the input lsit, the first element is always level 1 the second level 2 the third level 3 etc..
It should be done recursively, I tried few times but I have no idea how to assign to a nested list, specifically i need to do nested assigns.

Answer 1

I made the data into a matrix, transposed, then a dataframe:
x <- data.frame(t(vapply(categories, identity, character(3))), stringsAsFactors = F)
Then split, and lapply. You could do this recursively if you have more than 3 levels:
lapply(split(x, x$X1), function(df) {
lapply(split(df, df$X2), function(df) {
lapply(split(df, df$X3), function(x) list())
})
})

Answer 2

If you are looking for a recursive solution, then the following may help you:
output the full directory trajectory within a string at the end
## construct a data frame from list
df <- data.frame(matrix(unlist(categories),nrow = length(categories),byrow = T),stringsAsFactors = F)
## recursion function that makes nested list
f <- function(df, k=1) {
if (k == ncol(df)) return(lapply(split(df,df[,k]), toString)) ##
return(lapply(split(df,df[,k]), function(df) f(df, k+1)))
}
The nested list output looks as below
> f(df)
$Men
$Men$Accessories
$Men$Accessories$Belts
[1] "Men, Accessories, Belts"
$Women
$Women$Accessories
$Women$Accessories$Jewelry
[1] "Women, Accessories, Jewelry"
$Women$Clothing
$Women$Clothing$Jeans
[1] "Women, Clothing, Jeans"
$Women$Clothing$Sweaters
[1] "Women, Clothing, Sweaters"
output empty lists at the end
f <- function(df, k=1) {
if (k == ncol(df)) return(lapply(split(df,df[,k]), function(v) list()))
return(lapply(split(df,df[,k]), function(df) f(df, k+1)))
}
which gives:
> f(df)
$Men
$Men$Accessories
$Men$Accessories$Belts
list()
$Women
$Women$Accessories
$Women$Accessories$Jewelry
list()
$Women$Clothing
$Women$Clothing$Jeans
list()
$Women$Clothing$Sweaters
list()