r/R/Schema.R

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# to you under the Apache License, Version 2.0 (the
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#
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#
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#' @include R6.R

#' @title class arrow::Schema
#'
#' @usage NULL
#' @format NULL
#' @docType class
#'
#' @section Usage:
#'
#' ```
#' s <- schema(...)
#'
#' s$ToString()
#' s$num_fields()
#' s$field(i)
#' ```
#'
#' @section Methods:
#'
#' - `$ToString()`: convert to a string
#' - `$num_fields()`: returns the number of fields
#' - `$field(i)`: returns the field at index `i` (0-based)
#'
#' @rdname arrow__Schema
#' @name arrow__Schema
`arrow::Schema` <- R6Class("arrow::Schema",
  inherit = `arrow::Object`,
  public = list(
    ToString = function() Schema__ToString(self),
    num_fields = function() Schema__num_fields(self),
    field = function(i) shared_ptr(`arrow::Field`, Schema__field(self, i)),
    serialize = function() Schema__serialize(self),
    Equals = function(other, check_metadata = TRUE) Schema__Equals(self, other, isTRUE(check_metadata))
  ),
  active = list(
    names = function() Schema__names(self)
  )
)

#' @export
`==.arrow::Schema` <- function(lhs, rhs){
  lhs$Equals(rhs)
}

#' Schema factory
#'
#' @param ... named list of data types
#'
#' @return a [schema][arrow__Schema]
#'
#' @export
schema <- function(...){
  shared_ptr(`arrow::Schema`, schema_(.fields(list2(...))))
}

#' read a Schema from a stream
#'
#' @param stream a stream
#' @param ... currently ignored
#'
#' @export
read_schema <- function(stream, ...) {
  UseMethod("read_schema")
}

#' @export
`read_schema.arrow::io::InputStream` <- function(stream, ...) {
  shared_ptr(`arrow::Schema`, ipc___ReadSchema_InputStream(stream))
}

#' @export
`read_schema.arrow::Buffer` <- function(stream, ...) {
  stream <- BufferReader(stream)
  on.exit(stream$close())
  shared_ptr(`arrow::Schema`, ipc___ReadSchema_InputStream(stream))
}

#' @export
`read_schema.raw` <- function(stream, ...) {
  stream <- BufferReader(stream)
  on.exit(stream$close())
  shared_ptr(`arrow::Schema`, ipc___ReadSchema_InputStream(stream))
}

#' @export
`read_schema.arrow::ipc::Message` <- function(stream, ...) {
  shared_ptr(`arrow::Schema`, ipc___ReadSchema_Message(stream))
}