R list/dataframes to JSON array of objects - r

Question

I am trying to create a JSON array of objects using jsonlite in R.
The goal is a JSON like this:
{
"top":[
{
"master1": {
"item1": "value1"
}
},
{
"master2": {
"item2": "value2"
}
}
]
}
I tried list of lists and dataframes with list column but can't get the desired output.
Apart from that, converting the above with fromJSON/toJSON results in a different format:
library(jsonlite)
txt <- '{
"top":[
{
"master1": {
"item1": "value1"
}
},
{
"master2": {
"item2": "value2"
}
}]
}'
toJSON(fromJSON(txt), pretty = T)
# Output
{
"top": [
{
"master1": {
"item1": "value1"
},
"master2": {}
},
{
"master1": {},
"master2": {
"item2": "value2"
}
}
]
}
Do I need to set a parameter for this to work?

Answer 1

By default, the fromJSON call converts your input to a data frame, and therefore adds NA values, which result in the empty entries in your output JSON:
$top
item1 item2
1 value1 <NA>
2 <NA> value2
You need to add simplifyDataFrame = FALSE to the fromJSON call to prevent it from creating a data frame.
toJSON(fromJSON(txt, simplifyDataFrame = FALSE), pretty = T)
gives
{
"top": [
{
"master1": {
"item1": ["value1"]
}
},
{
"master2": {
"item2": ["value2"]
}
}
]
}