在R中提取嵌套数据值

Question

如何提取项目3如果我有一个嵌套的json列表像这样

[
 {
  "item1": null, 
  "item2": false, 
  "item3": "chr", 
  "item4": {
   "a": [], 
   "b": [
    {
     "a": 36659026, 
     "b": [
      3, 
      16
     ], 
     "c": "num"
    }, 
    {
  "item1": null, 
  "item2": false, 
  "item3": "chr", 
  "item4": {
   "a": [], 
   "b": [
    {
     "a": 36659026, 
     "b": [
      3, 
      16
     ], 
     "c": "num"
    },
    ]

我尝试过以下代码：

library(RJSONIO)
library(jsonlite)
# url with JSON content
data1 = "file.json"

data2 = readLines(data1)

#contacating all data into a single string
data2_str = paste(data2, collapse = "")

data3 = RJSONIO::fromJSON(data2_str)

我可以使用以下命令提取它3

 text.1 <- c(data3[[1]]$text)

但数据集中有500个item4如何提取所有这些。