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.

Usage

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.

Value

The input dataset, invisibly.

Usage

Arguments

Value

See also