"embedded" data.frame from JSON - json

Question

I have the following code, which extracts data from a JSON file.
library(jsonlite)
file_path <- 'C:/some/file/path.json'
df <- jsonlite::fromJSON(txt = file_path ,
simplifyVector = FALSE,
simplifyDataFrame = TRUE,
simplifyMatrix = FALSE,
flatten = FALSE)
The data structure is highly nested. My approach extracts 99% of it just fine, but in one particular part of the data I came across a phenomenon that I would describe as an "embedded" data frame:
df <- structure(
list(
ID = c(1L, 2L, 3L, 4L, 5L),
var1 = c('a', 'b', 'c', 'd', 'e'),
var2 = structure(
list(
var2a = c('v', 'w', 'x', 'y', 'z'),
var2b = c('vv', 'ww', 'xx', 'yy', 'zz')),
.Names = c('var2a', 'var2b'),
row.names = c(NA, 5L),
class = 'data.frame'),
var3 = c('aa', 'bb', 'cc', 'dd', 'ee')),
.Names = c('ID', 'var1', 'var2', 'var3'),
row.names = c(NA, 5L),
class = 'data.frame')
# Looks like this:
# ID var1 var2.var2a var2.var2b var3
# 1 1 a v vv aa
# 2 2 b w ww bb
# 3 3 c x xx cc
# 4 4 d y yy dd
# 5 5 e z zz ee
This looks like a normal data frame, and it behaves like that for the most part.
class(df)
# [1] "data.frame"
df[1,]
# ID var1 var2.var2a var2.var2b var3
# 1 a v vv aa
dim(df)
# [1] 5 4
# One less than expected due to embedded data frame
lapply(df, class)
# $ID
# [1] "integer"
#
# $var1
# [1] "character"
#
# $var2
# [1] "data.frame"
#
# $var3
# [1] "character"
str(df)
# 'data.frame': 5 obs. of 4 variables:
# $ ID : int 1 2 3 4 5
# $ var1: chr "a" "b" "c" "d" ...
# $ var2:'data.frame': 5 obs. of 2 variables:
# ..$ var2a: chr "v" "w" "x" "y" ...
# ..$ var2b: chr "vv" "ww" "xx" "yy" ...
# $ var3: chr "aa" "bb" "cc" "dd" ...
What is going on here, why is jsonlite creating this odd structure instead of just a simple data.frame? Can I avoid this behaviour, and if not how can I most elegantly rectify this? I've used the approach below, but it feels very hacky, at best.
# Any columns with embedded data frame?
newX <- X[,-which(lapply(X, class) == 'data.frame')] %>%
# Append them to the end
cbind(X[,which(lapply(X, class) == 'data.frame')])
Update
The suggested workaround solves my issue, but I still feel like I don't understand the strange embedded data.frame structure. I would have thought that such a structure would be illegal by R data format conventions, or at least behave differently in terms of subsetting using [. I have opened a separate question on that.

Answer 1

I think you want to flatten your df object:
json <- toJSON(df)
flat_df <- fromJSON(json, flatten = T)
str(flat_df)
'data.frame': 5 obs. of 5 variables:
$ ID : int 1 2 3 4 5
$ var1 : chr "a" "b" "c" "d" ...
$ var3 : chr "aa" "bb" "cc" "dd" ...
$ var2.var2a: chr "v" "w" "x" "y" ...
$ var2.var2b: chr "vv" "ww" "xx" "yy" ...
Is that closer to what you're looking for?