r/R/feather.R

# Licensed to the Apache Software Foundation (ASF) under one
# or more contributor license agreements.  See the NOTICE file
# distributed with this work for additional information
# regarding copyright ownership.  The ASF licenses this file
# to you under the Apache License, Version 2.0 (the
# "License"); you may not use this file except in compliance
# with the License.  You may obtain a copy of the License at
#
#   http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing,
# software distributed under the License is distributed on an
# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
# KIND, either express or implied.  See the License for the
# specific language governing permissions and limitations
# under the License.

#' Write data in the Feather format
#'
#' @param x `data.frame` or RecordBatch
#' @param sink A file path or an OutputStream
#'
#' @export
#' @examples
#' \donttest{
#' try({
#'   tf <- tempfile()
#'   on.exit(unlink(tf))
#'   write_feather(mtcars, tf)
#' })
#' }
#' @include arrow-package.R
write_feather <- function(x, sink) {
  if (is.data.frame(x)) {
    x <- record_batch(x)
  }
  assert_is(x, "RecordBatch")

  if (is.character(sink)) {
    sink <- FileOutputStream$create(sink)
    on.exit(sink$close())
  }
  assert_is(sink, "OutputStream")

  writer <- FeatherTableWriter$create(sink)
  ipc___TableWriter__RecordBatch__WriteFeather(writer, x)
}

#' @title FeatherTableWriter class
#' @rdname FeatherTableWriter
#' @name FeatherTableWriter
#' @docType class
#' @usage NULL
#' @format NULL
#' @description This class enables you to write Feather files. See its usage in
#' [write_feather()].
#'
#' @section Factory:
#'
#' The `FeatherTableWriter$create()` factory method instantiates the object and
#' takes the following argument:
#'
#' - `stream` An `OutputStream`
#'
#' @section Methods:
#'
#' - `$GetDescription()`
#' - `$HasDescription()`
#' - `$version()`
#' - `$num_rows()`
#' - `$num_columns()`
#' - `$GetColumnName()`
#' - `$GetColumn()`
#' - `$Read(columns)`
#'
#' @export
#' @include arrow-package.R
FeatherTableWriter <- R6Class("FeatherTableWriter", inherit = Object,
  public = list(
    SetDescription = function(description) ipc___feather___TableWriter__SetDescription(self, description),
    SetNumRows = function(num_rows) ipc___feather___TableWriter__SetNumRows(self, num_rows),
    Append = function(name, values) ipc___feather___TableWriter__Append(self, name, values),
    Finalize = function() ipc___feather___TableWriter__Finalize(self)
  )
)

FeatherTableWriter$create <- function(stream) {
  assert_is(stream, "OutputStream")
  unique_ptr(FeatherTableWriter, ipc___feather___TableWriter__Open(stream))
}

#' Read a Feather file
#'
#' @param file A character file path, a raw vector, or `InputStream`, passed to
#' `FeatherTableReader$create()`.
#' @inheritParams read_delim_arrow
#' @param ... additional parameters
#'
#' @return A `data.frame` if `as_data_frame` is `TRUE` (the default), or an
#' [arrow::Table][Table] otherwise
#'
#' @export
#' @examples
#' \donttest{
#' try({
#'   tf <- tempfile()
#'   on.exit(unlink(tf))
#'   write_feather(iris, tf)
#'   df <- read_feather(tf)
#'   dim(df)
#'   # Can select columns
#'   df <- read_feather(tf, col_select = starts_with("Sepal"))
#' })
#' }
read_feather <- function(file, col_select = NULL, as_data_frame = TRUE, ...) {
  reader <- FeatherTableReader$create(file, ...)

  all_columns <- ipc___feather___TableReader__column_names(reader)
  col_select <- enquo(col_select)
  columns <- if (!quo_is_null(col_select)) {
    vars_select(all_columns, !!col_select)
  }

  out <- reader$Read(columns)
  if (isTRUE(as_data_frame)) {
    out <- as.data.frame(out)
  }
  out
}

#' @title FeatherTableReader class
#' @rdname FeatherTableReader
#' @name FeatherTableReader
#' @docType class
#' @usage NULL
#' @format NULL
#' @description This class enables you to interact with Feather files. Create
#' one to connect to a file or other InputStream, and call `Read()` on it to
#' make an `arrow::Table`. See its usage in [`read_feather()`].
#'
#' @section Factory:
#'
#' The `FeatherTableReader$create()` factory method instantiates the object and
#' takes the following arguments:
#'
#' - `file` A character file name, raw vector, or Arrow file connection object
#'    (e.g. `RandomAccessFile`).
#' - `mmap` Logical: whether to memory-map the file (default `TRUE`)
#' - `...` Additional arguments, currently ignored
#'
#' @section Methods:
#'
#' - `$GetDescription()`
#' - `$HasDescription()`
#' - `$version()`
#' - `$num_rows()`
#' - `$num_columns()`
#' - `$GetColumnName()`
#' - `$GetColumn()`
#' - `$Read(columns)`
#'
#' @export
#' @include arrow-package.R
FeatherTableReader <- R6Class("FeatherTableReader", inherit = Object,
  public = list(
    GetDescription = function() ipc___feather___TableReader__GetDescription(self),
    HasDescription = function() ipc__feather___TableReader__HasDescription(self),
    version = function() ipc___feather___TableReader__version(self),
    num_rows = function() ipc___feather___TableReader__num_rows(self),
    num_columns = function() ipc___feather___TableReader__num_columns(self),
    GetColumnName = function(i) ipc___feather___TableReader__GetColumnName(self, i),
    GetColumn = function(i) shared_ptr(Array, ipc___feather___TableReader__GetColumn(self, i)),
    Read = function(columns) {
      shared_ptr(Table, ipc___feather___TableReader__Read(self, columns))
    }
  )
)

FeatherTableReader$create <- function(file, mmap = TRUE, ...) {
  file <- make_readable_file(file, mmap)
  unique_ptr(FeatherTableReader, ipc___feather___TableReader__Open(file))
}