fromJSON function

Convert objects to/from JSON

These functions are used to convert between JSON data and 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).

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
• x: 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'
• na: 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 (default is 2). Use a negative number for tabs instead of spaces.
• 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 objects and JSON strings.

The serializeJSON() and unserializeJSON() functions in this package use an alternative system to convert between 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.

Examples

# 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))
## End(Not run)

References

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

See Also

read_json(), stream_in()