R/field.R

In arrow: Integration to 'Apache' 'Arrow'

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#' @include arrow-object.R
#' @title Field class
#' @usage NULL
#' @format NULL
#' @docType class
#' @description `field()` lets you create an `arrow::Field` that maps a
#' [DataType][data-type] to a column name. Fields are contained in
#' [Schemas][Schema].
#' @section Methods:
#'
#' - `f$ToString()`: convert to a string
#' - `f$Equals(other, check_metadata = FALSE)`: test for equality.
#'    More naturally called as `f == other`
#' - `f$WithMetadata(metadata)`: returns a new `Field` with the key-value
#'    `metadata` set. Note that all list elements in `metadata` will be coerced
#'    to `character`.
#' - `f$RemoveMetadata()`: returns a new `Field` without metadata.
#'
#' @section Active bindings:
#'
#' - `$HasMetadata`: logical: does this `Field` have extra metadata?
#' - `$metadata`: returns the key-value metadata as a named list, or `NULL`
#'    if no metadata is set.
#'
#' @name Field
#' @rdname Field-class
#' @export
Field <- R6Class(
  "Field",
  inherit = ArrowObject,
  public = list(
    ToString = function() {
      prettier_dictionary_type(Field__ToString(self))
    },
    Equals = function(other, check_metadata = FALSE, ...) {
      inherits(other, "Field") && Field__Equals(self, other, isTRUE(check_metadata))
    },
    WithMetadata = function(metadata = NULL) {
      metadata <- prepare_key_value_metadata(metadata)
      Field__WithMetadata(self, metadata)
    },
    RemoveMetadata = function() {
      Field__RemoveMetadata(self)
    },
    export_to_c = function(ptr) ExportField(self, ptr)
  ),
  active = list(
    name = function() {
      Field__name(self)
    },
    nullable = function() {
      Field__nullable(self)
    },
    type = function() {
      Field__type(self)
    },
    HasMetadata = function() {
      Field__HasMetadata(self)
    },
    metadata = function() {
      if (self$HasMetadata) {
        as.list(Field__metadata(self))
      } else {
        NULL
      }
    }
  )
)
Field$create <- function(name, type, metadata = NULL, nullable = TRUE) {
  assert_that(inherits(name, "character"), length(name) == 1L)
  type <- as_type(type, name)
  f <- Field__initialize(enc2utf8(name), type, nullable)
  if (!is.null(metadata)) {
    f <- f$WithMetadata(metadata)
  }
  f
}
#' @include arrowExports.R
Field$import_from_c <- ImportField

#' Create a Field
#'
#' @param name field name
#' @param type logical type, instance of [DataType]
#' @param metadata a named character vector or list to attach as field metadata.
#'   All values will be coerced to `character`.
#' @param nullable TRUE if field is nullable
#'
#' @examples
#' field("x", int32())
#' field("x", int32(), metadata = list(key = "value"))
#' @rdname Field
#' @seealso [Field]
#' @export
field <- Field$create

.fields <- function(.list, nullable = TRUE) {
  if (length(.list)) {
    assert_that(!is.null(nms <- names(.list)))
    map2(nms, .list, field)
  } else {
    list()
  }
}