what is the fundamental difference between jsonlite and rjson packages?

Question

The rjson::fromJSON() reads a file incorrectly while jsonlite::fromJSON() reads it fine. Here's a sample example.

file test.json contents:

{"name": "Sanjay",
"unit_price": 130848,
"amount": 11,
"up_to_data_sales": 45725}

the jsonlite fromJSON outputs:

jsonlite::fromJSON("test.json")
$name
[1] "Sanjay"

$unit_price
[1] 130848

$amount
[1] 11

$up_to_data_sales
[1] 45725

But the same throws an error in rjson package.

rjson::fromJSON("test.json") 

Error in rjson::fromJSON("test.json") :   parseTrue: expected to see 'true' - likely an unquoted string starting with 't'.

1. Why is this error coming?
2. What is the reason rjson package was launched when jsonlite existed?

Answer 1

Well:

stringdist::stringdist("rjson", "jsonlite")
## [1] 5

That's a modest difference to begin with.

However, your assertion seems to be amiss:

library(magrittr)

rjson::fromJSON('{"name": "Sanjay",
"unit_price": 130848,
"amount": 11,
"up_to_data_sales": 45725}') %>% str()
## List of 4
##  $ name            : chr "Sanjay"
##  $ unit_price      : num 130848
##  $ amount          : num 11
##  $ up_to_data_sales: num 45725

jsonlite::fromJSON('{"name": "Sanjay",
"unit_price": 130848,
"amount": 11,
"up_to_data_sales": 45725}') %>% str()
## List of 4
##  $ name            : chr "Sanjay"
##  $ unit_price      : int 130848
##  $ amount          : int 11
##  $ up_to_data_sales: int 45725

Apart from jsonlite using a more diminutive data type for the numbers, they both parse the JSON fine.

So there's an issue with your file that you failed to disclose in the question.

A further incorrect assertion

-rw-rw-r--  1 bob  staff      2690 Jul 30  2007 rjson_0.1.0.tar.gz
-rw-rw-r--  1 bob  staff    400196 Dec  3  2013 jsonlite_0.9.0.tar.gz

not to mention:

-rw-rw-r--  1 bob   staff   873843 Oct  4  2010 RJSONIO_0.3-1.tar.gz

rjson came first. (dir listings came from the CRAN mirror sitting next to me).

You can actually read about the rationale and impetus behind jsonlite here: https://arxiv.org/abs/1403.2805 (which I got off the CRAN page for jsonlite.

Answer 2

1) Why is the error coming? - Error is due to the mistake in syntax

rjson does not read the file if 'file=' command is not given whereas when reading the file using Jsonlite it is not required

 # For example:

 y <- rjson::fromJSON(file = "Input.json") 
 x <- jsonlite::fromJSON("Input.json")

2) What is the reason rjson package was launched when jsonlite existed?

First, rjson was launched before jsonlite and second, there is a difference in the way they read files:

For example, consider the following input:

{ "id": 1, "prod_info": [ { "product": "xyz", "brand": "pqr", "price": 500 }, { "product": "abc", "brand": "klm", "price": 5000 } ] }

prod_info in the above input is a list with 2 vectors. But jsonlite reads it in the form of dataframe while rjson reads it as a list

Outputs:

x
$id
[1] 1

$prod_info
  product brand price
1     xyz   pqr   500
2     abc   klm  5000

y
$id
[1] 1

$prod_info
$prod_info[[1]]
$prod_info[[1]]$product
[1] "xyz"

$prod_info[[1]]$brand
[1] "pqr"

$prod_info[[1]]$price
[1] 500


$prod_info[[2]]
$prod_info[[2]]$product
[1] "abc"

$prod_info[[2]]$brand
[1] "klm"

$prod_info[[2]]$price
[1] 5000

class(x$prod_info)
[1] "data.frame"

class(y$prod_info)
[1] "list"

Answer 3

The question has already been answered, but regarding differences between the two packages, I got bitten by one recently: how empty dictionaries are handled.

With rjson

> rjson::fromJSON("[]")
list()
> rjson::fromJSON("{}")
list()

Whereas, with jsonlite:

> jsonlite::fromJSON("[]")
list()
> jsonlite::fromJSON("{}")
named list()

That is, with rjson, you can't tell the difference between an empty list and an empty dictionary.

The translation to JSON works with both however, e.g. toJSON(structure(list(), names=character(0))) yields "{}".