r/R/json.R

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# 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.

#' Read a JSON file
#'
#' Wrapper around [JsonTableReader] to read a newline-delimited JSON (ndjson) file into a
#' data frame or Arrow Table.
#'
#' If passed a path, will detect and handle compression from the file extension
#' (e.g. `.json.gz`).
#'
#' If `schema` is not provided, Arrow data types are inferred from the data:
#' - JSON null values convert to the [null()] type, but can fall back to any other type.
#' - JSON booleans convert to [boolean()].
#' - JSON numbers convert to [int64()], falling back to [float64()] if a non-integer is encountered.
#' - JSON strings of the kind "YYYY-MM-DD" and "YYYY-MM-DD hh:mm:ss" convert to [`timestamp(unit = "s")`][timestamp()],
#'   falling back to [utf8()] if a conversion error occurs.
#' - JSON arrays convert to a [list_of()] type, and inference proceeds recursively on the JSON arrays' values.
#' - Nested JSON objects convert to a [struct()] type, and inference proceeds recursively on the JSON objects' values.
#'
#' When `as_data_frame = TRUE`, Arrow types are further converted to R types.
#'
#' @inheritParams read_delim_arrow
#' @param schema [Schema] that describes the table.
#' @param ... Additional options passed to `JsonTableReader$create()`
#'
#' @return A `data.frame`, or a Table if `as_data_frame = FALSE`.
#' @export
#' @examplesIf arrow_with_json()
#' tf <- tempfile()
#' on.exit(unlink(tf))
#' writeLines('
#'     { "hello": 3.5, "world": false, "yo": "thing" }
#'     { "hello": 3.25, "world": null }
#'     { "hello": 0.0, "world": true, "yo": null }
#'   ', tf, useBytes = TRUE)
#'
#' read_json_arrow(tf)
#'
#' # Read directly from strings with `I()`
#' read_json_arrow(I(c('{"x": 1, "y": 2}', '{"x": 3, "y": 4}')))
read_json_arrow <- function(file,
                            col_select = NULL,
                            as_data_frame = TRUE,
                            schema = NULL,
                            ...) {
  if (inherits(file, "AsIs")) {
    if (is.raw(file)) {
      file <- unclass(file)
    } else {
      file <- charToRaw(paste(file, collapse = "\n"))
    }
  }

  if (!inherits(file, "InputStream")) {
    compression <- detect_compression(file)
    file <- make_readable_file(file)
    if (compression != "uncompressed") {
      # TODO: accept compression and compression_level as args
      file <- CompressedInputStream$create(file, compression)
    }
    on.exit(file$close())
  }
  tab <- JsonTableReader$create(file, schema = schema, ...)$Read()

  col_select <- enquo(col_select)
  if (!quo_is_null(col_select)) {
    sim_df <- as.data.frame(tab$schema)
    tab <- tab[eval_select(col_select, sim_df)]
  }

  if (isTRUE(as_data_frame)) {
    tab <- collect.ArrowTabular(tab)
  }
  tab
}

#' @include arrow-object.R
#' @rdname CsvTableReader
#' @usage NULL
#' @format NULL
#' @docType class
#' @export
JsonTableReader <- R6Class("JsonTableReader",
  inherit = ArrowObject,
  public = list(
    Read = function() json___TableReader__Read(self)
  )
)
JsonTableReader$create <- function(file,
                                   read_options = JsonReadOptions$create(),
                                   parse_options = JsonParseOptions$create(schema = schema),
                                   schema = NULL,
                                   ...) {
  assert_is(file, "InputStream")
  json___TableReader__Make(file, read_options, parse_options)
}

#' @rdname CsvReadOptions
#' @usage NULL
#' @format NULL
#' @docType class
#' @export
JsonReadOptions <- R6Class("JsonReadOptions", inherit = ArrowObject)
JsonReadOptions$create <- function(use_threads = option_use_threads(), block_size = 1048576L) {
  json___ReadOptions__initialize(use_threads, block_size)
}

#' @rdname CsvReadOptions
#' @usage NULL
#' @format NULL
#' @docType class
#' @export
JsonParseOptions <- R6Class("JsonParseOptions", inherit = ArrowObject)
JsonParseOptions$create <- function(newlines_in_values = FALSE, schema = NULL) {
  if (is.null(schema)) {
    json___ParseOptions__initialize1(newlines_in_values)
  } else {
    json___ParseOptions__initialize2(newlines_in_values, schema)
  }
}