as.yaml: Convert an R object into a YAML string

In yaml: Methods to Convert R Data to YAML and Back

Convert an R object into a YAML string

Description

Convert an R object into a YAML string

Usage

  as.yaml(x, line.sep = c("\n", "\r\n", "\r"), indent = 2, omap = FALSE,
          column.major = TRUE, unicode = TRUE, precision = getOption('digits'),
          indent.mapping.sequence = FALSE, handlers = NULL)

Arguments

Details

If you set the omap option to TRUE, as.yaml will create ordered maps (or omaps) instead of normal maps.

The column.major option determines how a data frame is converted. If TRUE, the data frame is converted into a map of sequences where the name of each column is a key. If FALSE, the data frame is converted into a sequence of maps, where each element in the sequence is a row. You'll probably almost always want to leave this as TRUE (which is the default), because using yaml.load on the resulting string returns an object which is much more easily converted into a data frame via as.data.frame.

You can specify custom handler functions via the handlers argument. This argument must be a named list of functions, where the names are R object class names (i.e., 'numeric', 'data.frame', 'list', etc). The function(s) you provide will be passed one argument (the R object) and can return any R object. The returned object will be emitted normally.

Character vectors that have a class of ‘verbatim’ will not be quoted in the output YAML document except when the YAML specification requires it. This means that you cannot do anything that would result in an invalid YAML document, but you can emit strings that would otherwise be quoted. This is useful for changing how logical vectors are emitted (see below for example).

Character vectors that have an attribute of ‘quoted’ will be wrapped in double quotes (see below for example).

You can specify YAML tags for R objects by setting the ‘tag’ attribute to a character vector of length 1. If you set a tag for a vector, the tag will be applied to the YAML sequence as a whole, unless the vector has only 1 element. If you wish to tag individual elements, you must use a list of 1-length vectors, each with a tag attribute. Likewise, if you set a tag for an object that would be emitted as a YAML mapping (like a data frame or a named list), it will be applied to the mapping as a whole. Tags can be used in conjunction with YAML deserialization functions like yaml.load via custom handlers, however, if you set an internal tag on an incompatible data type (like “!seq 1.0”), errors will occur when you try to deserialize the document.

Value

Returns a YAML string which can be loaded using yaml.load or copied into a file for external use.

Author(s)

Jeremy Stephens <jeremy.f.stephens@vumc.org>

References

YAML: http://yaml.org

YAML omap type: http://yaml.org/type/omap.html

See Also

yaml.load

Examples

  as.yaml(1:10)
  as.yaml(list(foo=1:10, bar=c("test1", "test2")))
  as.yaml(list(foo=1:10, bar=c("test1", "test2")), indent=3)
  as.yaml(list(foo=1:10, bar=c("test1", "test2")), indent.mapping.sequence=TRUE)
  as.yaml(data.frame(a=1:10, b=letters[1:10], c=11:20))
  as.yaml(list(a=1:2, b=3:4), omap=TRUE)
  as.yaml("multi\nline\nstring")
  as.yaml(function(x) x + 1)
  as.yaml(list(foo=list(list(x = 1, y = 2), list(x = 3, y = 4))))

  # custom handler
  as.yaml(Sys.time(), handlers = list(
    POSIXct = function(x) format(x, "%Y-%m-%d")
  ))

  # custom handler with verbatim output to change how logical vectors are
  # emitted
  as.yaml(c(TRUE, FALSE), handlers = list(
    logical = verbatim_logical))

  # force quotes around a string
  port_def <- "80:80"
  attr(port_def, "quoted") <- TRUE
  x <- list(ports = list(port_def))
  as.yaml(x)

  # custom tag for scalar
  x <- "thing"
  attr(x, "tag") <- "!thing"
  as.yaml(x)

  # custom tag for sequence
  x <- 1:10
  attr(x, "tag") <- "!thing"
  as.yaml(x)

  # custom tag for mapping
  x <- data.frame(a = letters[1:5], b = letters[6:10])
  attr(x, "tag") <- "!thing"
  as.yaml(x)

  # custom tag for each element in a list
  x <- list(1, 2, 3)
  attr(x[[1]], "tag") <- "!a"
  attr(x[[2]], "tag") <- "!b"
  attr(x[[3]], "tag") <- "!c"
  as.yaml(x)