toJSON, fromJSON: Convert R objects to/from JSON

Description

These functions are used to convert between JSON data and R objects. The toJSON() and fromJSON() functions use a class based mapping, which follows conventions outlined in this paper: https://arxiv.org/abs/1403.2805 (also available as vignette).

Usage

fromJSON(
  txt,
  simplifyVector = TRUE,
  simplifyDataFrame = simplifyVector,
  simplifyMatrix = simplifyVector,
  flatten = FALSE,
  ...
)
toJSON(
  x,
  dataframe = c("rows", "columns", "values"),
  matrix = c("rowmajor", "columnmajor"),
  Date = c("ISO8601", "epoch"),
  POSIXt = c("string", "ISO8601", "epoch", "mongo"),
  factor = c("string", "integer"),
  complex = c("string", "list"),
  raw = c("base64", "hex", "mongo", "int", "js"),
  null = c("list", "null"),
  na = c("null", "string"),
  auto_unbox = FALSE,
  digits = 4,
  pretty = FALSE,
  force = FALSE,
  ...
)

Arguments

txt

a JSON string, URL or file

simplifyVector

coerce JSON arrays containing only primitives into an atomic vector

simplifyDataFrame

coerce JSON arrays containing only records (JSON objects) into a data frame

simplifyMatrix

coerce JSON arrays containing vectors of equal mode and dimension into matrix or array

flatten

automatically flatten() nested data frames into a single non-nested data frame

...

arguments passed on to class specific print methods

the object to be encoded

dataframe

how to encode data.frame objects: must be one of 'rows', 'columns' or 'values'

matrix

how to encode matrices and higher dimensional arrays: must be one of 'rowmajor' or 'columnmajor'.

Date

how to encode Date objects: must be one of 'ISO8601' or 'epoch'

POSIXt

how to encode POSIXt (datetime) objects: must be one of 'string', 'ISO8601', 'epoch' or 'mongo'

factor

how to encode factor objects: must be one of 'string' or 'integer'

complex

how to encode complex numbers: must be one of 'string' or 'list'

raw

how to encode raw objects: must be one of 'base64', 'hex' or 'mongo'

null

how to encode NULL values within a list: must be one of 'null' or 'list'

how to print NA values: must be one of 'null' or 'string'. Defaults are class specific

auto_unbox

automatically unbox() all atomic vectors of length 1. It is usually safer to avoid this and instead use the unbox() function to unbox individual elements. An exception is that objects of class AsIs (i.e. wrapped in I()) are not automatically unboxed. This is a way to mark single values as length-1 arrays.

digits

max number of decimal digits to print for numeric values. Use I() to specify significant digits. Use NA for max precision.

pretty

adds indentation whitespace to JSON output. Can be TRUE/FALSE or a number specifying the number of spaces to indent. See prettify()

force

unclass/skip objects of classes with no defined JSON mapping

Details

The toJSON() and fromJSON() functions are drop-in replacements for the identically named functions in packages rjson and RJSONIO. Our implementation uses an alternative, somewhat more consistent mapping between R objects and JSON strings.

The serializeJSON() and unserializeJSON() functions in this package use an alternative system to convert between R objects and JSON, which supports more classes but is much more verbose.

A JSON string is always unicode, using UTF-8 by default, hence there is usually no need to escape any characters. However, the JSON format does support escaping of unicode characters, which are encoded using a backslash followed by a lower case "u" and 4 hex characters, for example: "Z\u00FCrich". The fromJSON function will parse such escape sequences but it is usually preferable to encode unicode characters in JSON using native UTF-8 rather than escape sequences.

References

Jeroen Ooms (2014). The jsonlite Package: A Practical and Consistent Mapping Between JSON Data and R Objects. arXiv:1403.2805. https://arxiv.org/abs/1403.2805

Examples

Run this code

# NOT RUN {
# Stringify some data
jsoncars <- toJSON(mtcars, pretty=TRUE)
cat(jsoncars)

# Parse it back
fromJSON(jsoncars)

# Parse escaped unicode
fromJSON('{"city" : "Z\\u00FCrich"}')

# Decimal vs significant digits
toJSON(pi, digits=3)
toJSON(pi, digits=I(3))

# }
# NOT RUN {
#retrieve data frame
data1 <- fromJSON("https://api.github.com/users/hadley/orgs")
names(data1)
data1$login

# Nested data frames:
data2 <- fromJSON("https://api.github.com/users/hadley/repos")
names(data2)
names(data2$owner)
data2$owner$login

# Flatten the data into a regular non-nested dataframe
names(flatten(data2))

# Flatten directly (more efficient):
data3 <- fromJSON("https://api.github.com/users/hadley/repos", flatten = TRUE)
identical(data3, flatten(data2))
# }