R/get_unitList.R

In EML: Read and Write Ecological Metadata Language Files

#' get_unitList
#' @param x an emld object
#' @return a list with two data.frames: "units", a table defining unit names, types, and conversions to SI,
#' and "unitTypes", defining the type of unit. For instance, the unit table could define "Hertz" as a unit
#' of unitType frequency, and the unitType define frequency as a type whose dimension is 1/time.
#'
#' @details If no unitList is provided, the function reads in the eml-unitDictionary defining all standard
#' units and unitTypes.  This provides a convenient way to look up standard units and their EML-recognized names
#' when defining metadata, e.g. in the table passed to `set_attributes()`.
#' @export
#'
#' @examples
#'
#' # Read in additional units defined in a EML file
#' \donttest{
#' f <- system.file("tests", emld::eml_version(),
#'   "eml-datasetWithUnits.xml",
#'   package = "emld"
#' )
#' eml <- read_eml(f)
#' unitList <- get_unitList(eml)
#'
#' ## Read in the definitions of standard units:
#' get_unitList()
#' }
#'
get_unitList <-
  function(x = NULL) {
    if (is.null(x)) {
      unitList <- read_eml(system.file("tests",
                                       emld::eml_version(),
                                       "eml-unitDictionary.xml",
                                       package = "emld"
      ))
    } else {
      unitList <- eml_get(x, "unitList")
    }
    list(
      units = get_unit(unitList$unit),
      unitTypes = get_unitType(unitList$unitType)
    )
  }



get_unit <- function(unit) {
  ## Unnested structure, easy to rectangle
  fromJSON(toJSON(unit, auto_unbox = T))
}

#' @importFrom jsonlite toJSON fromJSON
get_unitType <- function(unitType) {
  ## Nested data structure, rectangle via jq
  y <- toJSON(unitType, auto_unbox = T)

  tmp <- jqr::jq(as.character(y),
    ".[] | {
             id,
             name,
             dimension: .dimension[].name?,
             power: .dimension[].power?
            }")
  fromJSON(jqr::combine(tmp))
}