yaml.load

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Convert a YAML string into R objects

Parse a YAML string and return R objects.

Keywords
data, programming , manip
Usage
yaml.load(string, as.named.list = TRUE, handlers = NULL, error.label = NULL)
  yaml.load_file(input, error.label, ...)
Arguments
string

the YAML string to be parsed

as.named.list

whether or not to return a named list for maps (TRUE by default)

handlers

named list of custom handler functions for YAML types (see Details).

input

a filename or connection. If input is a filename, that file must be encoded in UTF-8.

error.label

a label to prepend to error messages (see Details).

...

arguments to pass to yaml.load

Details

Use yaml.load to load a YAML string. For files and connections, use yaml.load_file, which calls yaml.load with the contents of the specified file or connection.

Sequences of uniform data (e.g. a sequence of integers) are converted into vectors. If the sequence is not uniform, it's returned as a list. Maps are converted into named lists by default, and all the keys in the map are converted to strings. If you don't want the keys to be coerced into strings, set as.named.list to FALSE. When it's FALSE, a list will be returned with an additional attribute named 'keys', which is a list of the un-coerced keys in the map (in the same order as the main list).

You can specify custom handler functions via the handlers argument. This argument must be a named list of functions, where the names are the YAML types (i.e., 'int', 'float', 'seq', etc). The functions you provide will be passed one argument. Custom handler functions for string types (all types except sequence and map) will receive a character vector of length 1. Custom sequence functions will be passed a list of objects. Custom map functions will be passed the object that the internal map handler creates, which is either a named list or a list with a 'keys' attribute (depending on as.named.list). ALL functions you provide must return an object. See the examples for custom handler use.

You can specify a label to be prepended to error messages via the error.label argument. When using yaml.load_file, you can either set the error.label argument explicitly or leave it missing. If missing, yaml.load_file will make an educated guess for the value of error.label by either using the specified filename (when input is a character vector) or using the description of the supplied connection object (via the summary function). You can explicity set error.label to NULL if you don't want to use this functionality.

This function uses the YAML parser provided by libyaml, which conforms to the YAML 1.1 specification.

Value

If the root YAML object is a map, a named list or list with an attribute of 'keys' is returned. If the root object is a sequence, a list or vector is returned, depending on the contents of the sequence. A vector of length 1 is returned for single objects.

References

YAML: http://yaml.org

libyaml: http://pyyaml.org/wiki/LibYAML

See Also

as.yaml

Aliases
  • yaml.load
  • yaml.load_file
Examples
# NOT RUN {
  yaml.load("- hey\n- hi\n- hello")
  yaml.load("foo: 123\nbar: 456")
  yaml.load("- foo\n- bar\n- 3.14")
  yaml.load("foo: bar\n123: 456", as.named.list = FALSE)

# }
# NOT RUN {
  # reading from a file (uses readLines internally)
  cat("foo: 123", file="foo.yml", sep="\n")
  yaml.load_file('foo.yml')
  unlink("foo.yml") # tidy up
# }
# NOT RUN {
  # custom scalar handler
  my.float.handler <- function(x) { as.numeric(x) + 123 }
  yaml.load("123.456", handlers=list("float#fix"=my.float.handler))

  # custom sequence handler
  yaml.load("- 1\n- 2\n- 3", handlers=list(seq=function(x) { as.integer(x) + 3 }))

  # custom map handler
  yaml.load("foo: 123", handlers=list(map=function(x) { x$foo <- x$foo + 123; x }))

  # handling custom types
  yaml.load("!sqrt 555", handlers=list(sqrt=function(x) { sqrt(as.integer(x)) }))
  yaml.load("!foo\n- 1\n- 2", handlers=list(foo=function(x) { as.integer(x) + 1 }))
  yaml.load("!bar\none: 1\ntwo: 2", handlers=list(foo=function(x) { x$one <- "one"; x }))

  # loading R expressions
  # NOTE: this will not be done by default in the near future
  doc <- yaml.load("inc: !expr function(x) x + 1")
  doc$inc(1)

  # adding a label to error messages
  try(yaml.load("*", error.label = "foo"))
# }
Documentation reproduced from package yaml, version 2.1.17, License: BSD_3_clause + file LICENSE

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