r/R/scalar.R

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#' @include arrow-package.R

#' @title Arrow scalars
#' @usage NULL
#' @format NULL
#' @docType class
#'
#' @description A `Scalar` holds a single value of an Arrow type.
#'
#' @name Scalar
#' @rdname Scalar
#' @export
Scalar <- R6Class("Scalar",
  inherit = ArrowObject,
  # TODO: document the methods
  public = list(
    ..dispatch = function() {
      type_id <- self$type$id
      if (type_id == Type$STRUCT) {
        shared_ptr(StructScalar, self$pointer())
      } else {
        self
      }
    },
    ToString = function() Scalar__ToString(self),
    cast = function(target_type) {
      Scalar$create(Scalar__CastTo(self, as_type(target_type)))
    },
    as_vector = function() Scalar__as_vector(self)
  ),
  active = list(
    is_valid = function() Scalar__is_valid(self),
    null_count = function() sum(!self$is_valid),
    type = function() DataType$create(Scalar__type(self))
  )
)
Scalar$create <- function(x, type = NULL) {
  if (!inherits(x, "externalptr")) {
    if (is.null(x)) {
      x <- vctrs::unspecified(1)
    } else if (length(x) != 1 && !is.data.frame(x)) {
      # Wrap in a list type
      x <- list(x)
    }
    x <- Array__GetScalar(Array$create(x, type = type), 0)
  }
  shared_ptr(Scalar, x)$..dispatch()
}

#' @rdname array
#' @usage NULL
#' @format NULL
#' @export
StructScalar <- R6Class("StructScalar",
  inherit = Scalar,
  public = list(
    field = function(i) Scalar$create(StructScalar__field(self, i)),
    GetFieldByName = function(name) Scalar$create(StructScalar__GetFieldByName(self, name))
  )
)

#' @export
length.Scalar <- function(x) 1L

#' @export
is.na.Scalar <- function(x) !x$is_valid

#' @export
as.vector.Scalar <- function(x, mode) x$as_vector()

#' @export
as.double.Scalar <- as.double.Array

#' @export
as.integer.Scalar <- as.integer.Array

#' @export
as.character.Scalar <- as.character.Array