write_delim_dataset function

Write a dataset into partitioned flat files.

The write_*_dataset() are a family of wrappers around write_dataset to allow for easy switching between functions for writing datasets.

write_delim_dataset(
  dataset,
  path,
  partitioning = dplyr::group_vars(dataset),
  basename_template = "part-{i}.txt",
  hive_style = TRUE,
  existing_data_behavior = c("overwrite", "error", "delete_matching"),
  max_partitions = 1024L,
  max_open_files = 900L,
  max_rows_per_file = 0L,
  min_rows_per_group = 0L,
  max_rows_per_group = bitwShiftL(1, 20),
  col_names = TRUE,
  batch_size = 1024L,
  delim = ",",
  na = "",
  eol = "\n",
  quote = c("needed", "all", "none")
)

write_csv_dataset(
  dataset,
  path,
  partitioning = dplyr::group_vars(dataset),
  basename_template = "part-{i}.csv",
  hive_style = TRUE,
  existing_data_behavior = c("overwrite", "error", "delete_matching"),
  max_partitions = 1024L,
  max_open_files = 900L,
  max_rows_per_file = 0L,
  min_rows_per_group = 0L,
  max_rows_per_group = bitwShiftL(1, 20),
  col_names = TRUE,
  batch_size = 1024L,
  delim = ",",
  na = "",
  eol = "\n",
  quote = c("needed", "all", "none")
)

write_tsv_dataset(
  dataset,
  path,
  partitioning = dplyr::group_vars(dataset),
  basename_template = "part-{i}.tsv",
  hive_style = TRUE,
  existing_data_behavior = c("overwrite", "error", "delete_matching"),
  max_partitions = 1024L,
  max_open_files = 900L,
  max_rows_per_file = 0L,
  min_rows_per_group = 0L,
  max_rows_per_group = bitwShiftL(1, 20),
  col_names = TRUE,
  batch_size = 1024L,
  na = "",
  eol = "\n",
  quote = c("needed", "all", "none")
)

Arguments

• dataset: Dataset , RecordBatch , Table , arrow_dplyr_query, or data.frame. If an arrow_dplyr_query, the query will be evaluated and the result will be written. This means that you can select(), filter(), mutate(), etc. to transform the data before it is written if you need to.

• path: string path, URI, or SubTreeFileSystem referencing a directory to write to (directory will be created if it does not exist)

• partitioning: Partitioning or a character vector of columns to use as partition keys (to be written as path segments). Default is to use the current group_by() columns.

• basename_template: string template for the names of files to be written. Must contain "{i}", which will be replaced with an autoincremented integer to generate basenames of datafiles. For example, "part-{i}.arrow"

  will yield "part-0.arrow", .... If not specified, it defaults to "part-{i}.<default extension>".

• hive_style: logical: write partition segments as Hive-style (key1=value1/key2=value2/file.ext) or as just bare values. Default is TRUE.

• existing_data_behavior: The behavior to use when there is already data in the destination directory. Must be one of "overwrite", "error", or "delete_matching".

  • "overwrite" (the default) then any new files created will overwrite existing files
  • "error" then the operation will fail if the destination directory is not empty
  • "delete_matching" then the writer will delete any existing partitions if data is going to be written to those partitions and will leave alone partitions which data is not written to.

• max_partitions: maximum number of partitions any batch may be written into. Default is 1024L.

• max_open_files: maximum number of files that can be left opened during a write operation. If greater than 0 then this will limit the maximum number of files that can be left open. If an attempt is made to open too many files then the least recently used file will be closed. If this setting is set too low you may end up fragmenting your data into many small files. The default is 900 which also allows some # of files to be open by the scanner before hitting the default Linux limit of 1024.

• max_rows_per_file: maximum number of rows per file. If greater than 0 then this will limit how many rows are placed in any single file. Default is 0L.

• min_rows_per_group: write the row groups to the disk when this number of rows have accumulated. Default is 0L.

• max_rows_per_group: maximum rows allowed in a single group and when this number of rows is exceeded, it is split and the next set of rows is written to the next group. This value must be set such that it is greater than min_rows_per_group. Default is 1024 * 1024.

• col_names: Whether to write an initial header line with column names.

• batch_size: Maximum number of rows processed at a time. Default is 1024L.

• delim: Delimiter used to separate values. Defaults to "," for write_delim_dataset() and write_csv_dataset(), and "\t for write_tsv_dataset(). Cannot be changed for write_tsv_dataset().

• na: a character vector of strings to interpret as missing values. Quotes are not allowed in this string. The default is an empty string "".

• eol: the end of line character to use for ending rows. The default is "\n".

• quote: How to handle fields which contain characters that need to be quoted.

  • needed - Enclose all strings and binary values in quotes which need them, because their CSV rendering can contain quotes itself (the default)
  • all - Enclose all valid values in quotes. Nulls are not quoted. May cause readers to interpret all values as strings if schema is inferred.
  • none - Do not enclose any values in quotes. Prevents values from containing quotes ("), cell delimiters (,) or line endings (\r, \n), (following RFC4180). If values contain these characters, an error is caused when attempting to write.

Returns

The input dataset, invisibly.

See Also

write_dataset()