Convert R data.frame to multilevel JSON - json

Question

I have a periodic process in R that yields me a data.frame.
I want to use this data.frame to create a dropdown selector with AngularJS.
My final data.frame will look more or less as follows (my real example might have a deeper hierarchical structure):
DF<-data.frame(hie1=c(rep("Cl1",2),"Cl2"),hie2=c("Cl1op1","Cl1op2","Clop1"),
hie3=c("/first.html","/second.html","/third.html"))
I need to convert that data.frame into a JSON with the following structure :
{
"Cl1":{"Cl1op1":"/first.html","Cl1op2": "/second.html"},
"Cl2":{"Cl2op1":"/third.html"}
}
So far, I have tried all the toJSON commands of the rjson and RJSONIO packages for the data.frame with and without column names:
library(rjson)
#library(RJSONIO)
DF2<-DF
colnames(DF2)<-NULL
cat(toJSON(DF))
cat(toJSON(DF2))
I thought about using reshape2's dcast function beforeusing toJSON, but I do not know what kind of structure I need to achieve my goal.
I also used the functions toJSON2 an toJSONArray from the rCharts with no success.
Is there an appropriate transformation in R to get the output I am looking for?
P.S. (I do not mind having [] instead of {})
EDIT:
I have created a couple of functions (included below) to fulfil my needs.
However, they are not too clean and I believe that there must be a better way to perform this transformation in R.
I keep this question open expecting a better solution.
linktwo<-function(V){
paste0(sapply(V,function(x) paste0("'",toString(x),"'")),collapse=":")
}
pastehier<-function(DF){
if(ncol(DF)==2){
return(paste0(apply(DF,1,linktwo),collapse=","))
}else{
u<-unique(DF[,1])
output=character()
for(i in u){
output<-append(output,paste0(paste0("'",i,"'"),":{",pastehier(DF[DF[,1]==i,-1]),
"}"))
}
return(paste0(output,collapse=","))
}
}
pastehier(DF)

Answer 1

I do not fully understand your request and maybe my solution is useless, but here is a try:
library(reshape2)
prova <- dcast(DF, hie1 ~ ... )
toJSON(prova, pretty = TRUE)
[
{
"hie1": "Cl1",
"Cl1op1": "/first.html",
"Cl1op2": "/second.html"
},
{
"hie1": "Cl2",
"Clop1": "/third.html"
}
]
where:
> prova
hie1 Cl1op1 Cl1op2 Clop1
1 Cl1 /first.html /second.html <NA>
2 Cl2 <NA> <NA> /third.html