Converts 'R' Objects to Javascript Object Notation (JSON)

Converts 'R' objects into Javascript Object Notation (JSON) using the 'rapidjsonr' library < https://CRAN.R-project.org/package=rapidjsonr>.

jsonify converts R objects to JSON.

There are already JSON converters, why did you build this one?

Because I wanted it available at the source ( C++ ) level for integrating into other packages.

Is it fast?

It does alright

 
library(microbenchmark)
library(jsonlite)
 
n <- 5e6
df <- data.frame(
  id = 1:n
  , value = sample(letters, size = n, replace = T)
  , val2 = rnorm(n = n)
  , log = sample(c(T,F), size = n, replace = T)
)
 
microbenchmark(
  jsonlite = {
    js <- jsonlite::toJSON( df )
  },
  jsonify = {
    js <- jsonify::to_json( df )
  },
  times = 3
)
 
# Unit: seconds
#      expr       min        lq      mean    median        uq       max neval
#  jsonlite 11.243452 13.174676 14.721483 15.105899 16.460498 17.815098     3
#   jsonify  4.607378  4.696038  5.419219  4.784698  5.825139  6.865581     3
 
n <- 1e4
x <- list(
  x = rnorm(n = n)
  , y = list(x = rnorm(n = n))
  , z = list( list( x = rnorm(n = n)))
  , xx = rnorm(n = n)
  , yy = data.frame(
      id = 1:n
      , value = sample(letters, size = n, replace = T)
      , val2 = rnorm(n = n)
      , log = sample(c(T,F), size = n, replace = T)
    )
)
 
microbenchmark(
  jsonlite = {
    js <- jsonlite::toJSON( x )
  },
  jsonify = {
    js <- jsonify::to_json( x )
  },
  times = 5
)
 
# Unit: milliseconds
#      expr       min        lq      mean    median        uq       max neval
#  jsonlite 19.226906 19.488125 20.310911 19.768292 21.142979 21.928253     5
#   jsonify  7.638329  7.715288  7.944044  7.879122  7.924961  8.562521     5
   

There’s no Date type in JSON, how have you handled this?

At its core Dates in R are numeric, so they are treated as numbers when converted to JSON. However, the user can coerce to character through the numeric_dates argument.

This argument only works for data.frames and vectors, not lists

df <- data.frame(dte = as.Date("2018-01-01"))
jsonify::to_json( df )
#  [1] "[{\"dte\":17532.0}]"
#  attr(,"class")
#  [1] "json"
 
df <- data.frame(dte = as.Date("2018-01-01"))
jsonify::to_json( df, numeric_dates = FALSE )
#  [1] "[{\"dte\":\"2018-01-01\"}]"
#  attr(,"class")
#  [1] "json"
 
df <- data.frame(dte = as.POSIXct("2018-01-01 01:01:01"))
jsonify::to_json( df )
#  [1] "[{\"dte\":1514728861.0}]"
#  attr(,"class")
#  [1] "json"
 
df <- data.frame(dte = as.POSIXct("2018-01-01 01:01:01"))
jsonify::to_json( df, numeric_dates = FALSE )
#  [1] "[{\"dte\":\"2018-01-01 01:01:01\"}]"
#  attr(,"class")
#  [1] "json"

And POSIXct and POSIXlt?

POSIXct work the same as Date

df <- data.frame(dte = as.POSIXct("2018-01-01 10:00:00"))
jsonify::to_json( df )
#  [1] "[{\"dte\":1514761200.0}]"
#  attr(,"class")
#  [1] "json"
jsonify::to_json( df, numeric_dates = FALSE)
#  [1] "[{\"dte\":\"2018-01-01 10:00:00\"}]"
#  attr(,"class")
#  [1] "json"

POSIXlt will return each component of the date-time

x <- as.POSIXlt("2018-01-01 01:00:00", tz = "GMT")
jsonify::to_json( x )
#  [1] "{\"sec\":[0.0],\"min\":[0],\"hour\":[1],\"mday\":[1],\"mon\":[0],\"year\":[118],\"wday\":[1],\"yday\":[0],\"isdst\":[0]}"
#  attr(,"class")
#  [1] "json"
jsonify::to_json( x, numeric_dates = FALSE)
#  [1] "[\"2018-01-01 01:00:00\"]"
#  attr(,"class")
#  [1] "json"

What about lists?

The purpose of this library is speed. A lot of overhead is incurred iterating over a list to find and convert objects from one type to another.

What do you mean by “available at the source” ?

I want to be able to call the C++ code from another package, without going to & from R. Therefore, the C++ code is implemented in headers, so you can “link to” it in your own package.

For example, the LinkingTo section in DESCRIPTION will look something like

LinkingTo: 
    Rcpp,
    jsonify

And in a c++ source file you can #include the header and use the available functions

// [[Rcpp::depends(jsonify)]] 
#include "jsonify/to_json.hpp"
 
Rcpp::StringVector my_json( Rcpp::DataFrame df ) {
  return jsonify::to_json( df );
}

Can I call it from R if I want to?

Yes.

df <- data.frame(
  id = 1:3
  , val = letters[1:3]
  , stringsAsFactors = FALSE 
  )
jsonify::to_json( df )
#  [1] "[{\"id\":1,\"val\":\"a\"},{\"id\":2,\"val\":\"b\"},{\"id\":3,\"val\":\"c\"}]"
#  attr(,"class")
#  [1] "json"

How do I install it?

Install the development version from GitHub with:

# install.packages("devtools")
devtools::install_github("SymbolixAU/jsonify")