Open a multi-file dataset of CSV or other delimiter-separated format

A wrapper around open_dataset which explicitly includes parameters mirroring read_csv_arrow(), read_delim_arrow(), and read_tsv_arrow() to allow for easy switching between functions for opening single files and functions for opening datasets.

Usage

open_delim_dataset(
  sources,
  schema = NULL,
  partitioning = hive_partition(),
  hive_style = NA,
  unify_schemas = NULL,
  factory_options = list(),
  delim = ",",
  quote = "\"",
  escape_double = TRUE,
  escape_backslash = FALSE,
  col_names = TRUE,
  col_types = NULL,
  na = c("", "NA"),
  skip_empty_rows = TRUE,
  skip = 0L,
  convert_options = NULL,
  read_options = NULL,
  timestamp_parsers = NULL,
  quoted_na = TRUE,
  parse_options = NULL
)

open_csv_dataset(
  sources,
  schema = NULL,
  partitioning = hive_partition(),
  hive_style = NA,
  unify_schemas = NULL,
  factory_options = list(),
  quote = "\"",
  escape_double = TRUE,
  escape_backslash = FALSE,
  col_names = TRUE,
  col_types = NULL,
  na = c("", "NA"),
  skip_empty_rows = TRUE,
  skip = 0L,
  convert_options = NULL,
  read_options = NULL,
  timestamp_parsers = NULL,
  quoted_na = TRUE,
  parse_options = NULL
)

open_tsv_dataset(
  sources,
  schema = NULL,
  partitioning = hive_partition(),
  hive_style = NA,
  unify_schemas = NULL,
  factory_options = list(),
  quote = "\"",
  escape_double = TRUE,
  escape_backslash = FALSE,
  col_names = TRUE,
  col_types = NULL,
  na = c("", "NA"),
  skip_empty_rows = TRUE,
  skip = 0L,
  convert_options = NULL,
  read_options = NULL,
  timestamp_parsers = NULL,
  quoted_na = TRUE,
  parse_options = NULL
)

Arguments

sources

One of:

a string path or URI to a directory containing data files
a FileSystem that references a directory containing data files (such as what is returned by s3_bucket())
a string path or URI to a single file
a character vector of paths or URIs to individual data files
a list of Dataset objects as created by this function
a list of DatasetFactory objects as created by dataset_factory().

When sources is a vector of file URIs, they must all use the same protocol and point to files located in the same file system and having the same format.

schema

Schema for the Dataset. If NULL (the default), the schema will be inferred from the data sources.

partitioning

When sources is a directory path/URI, one of:

a Schema, in which case the file paths relative to sources will be parsed, and path segments will be matched with the schema fields.
a character vector that defines the field names corresponding to those path segments (that is, you're providing the names that would correspond to a Schema but the types will be autodetected)
a Partitioning or PartitioningFactory, such as returned by hive_partition()
NULL for no partitioning

The default is to autodetect Hive-style partitions unless hive_style = FALSE. See the "Partitioning" section for details. When sources is not a directory path/URI, partitioning is ignored.

hive_style

Logical: should partitioning be interpreted as Hive-style? Default is NA, which means to inspect the file paths for Hive-style partitioning and behave accordingly.

unify_schemas

logical: should all data fragments (files, Datasets) be scanned in order to create a unified schema from them? If FALSE, only the first fragment will be inspected for its schema. Use this fast path when you know and trust that all fragments have an identical schema. The default is FALSE when creating a dataset from a directory path/URI or vector of file paths/URIs (because there may be many files and scanning may be slow) but TRUE when sources is a list of Datasets (because there should be few Datasets in the list and their Schemas are already in memory).

factory_options

list of optional FileSystemFactoryOptions:

partition_base_dir: string path segment prefix to ignore when discovering partition information with DirectoryPartitioning. Not meaningful (ignored with a warning) for HivePartitioning, nor is it valid when providing a vector of file paths.
exclude_invalid_files: logical: should files that are not valid data files be excluded? Default is FALSE because checking all files up front incurs I/O and thus will be slower, especially on remote filesystems. If false and there are invalid files, there will be an error at scan time. This is the only FileSystemFactoryOption that is valid for both when providing a directory path in which to discover files and when providing a vector of file paths.
selector_ignore_prefixes: character vector of file prefixes to ignore when discovering files in a directory. If invalid files can be excluded by a common filename prefix this way, you can avoid the I/O cost of exclude_invalid_files. Not valid when providing a vector of file paths (but if you're providing the file list, you can filter invalid files yourself).

delim

Single character used to separate fields within a record.

quote

Single character used to quote strings.

escape_double

Does the file escape quotes by doubling them? i.e. If this option is TRUE, the value """" represents a single quote, \".

escape_backslash

Does the file use backslashes to escape special characters? This is more general than escape_double as backslashes can be used to escape the delimiter character, the quote character, or to add special characters like \\n.

col_names

If TRUE, the first row of the input will be used as the column names and will not be included in the data frame. If FALSE, column names will be generated by Arrow, starting with "f0", "f1", ..., "fN". Alternatively, you can specify a character vector of column names.

col_types

A compact string representation of the column types, an Arrow Schema, or NULL (the default) to infer types from the data.

na

A character vector of strings to interpret as missing values.

skip_empty_rows

Should blank rows be ignored altogether? If TRUE, blank rows will not be represented at all. If FALSE, they will be filled with missings.

skip

Number of lines to skip before reading data.

convert_options

see CSV conversion options

read_options

see CSV reading options

timestamp_parsers

User-defined timestamp parsers. If more than one parser is specified, the CSV conversion logic will try parsing values starting from the beginning of this vector. Possible values are:

NULL: the default, which uses the ISO-8601 parser
a character vector of strptime parse strings
a list of TimestampParser objects

quoted_na

Should missing values inside quotes be treated as missing values (the default) or strings. (Note that this is different from the the Arrow C++ default for the corresponding convert option, strings_can_be_null.)

parse_options

see CSV parsing options. If given, this overrides any parsing options provided in other arguments (e.g. delim, quote, etc.).

Options currently supported by `read_delim_arrow()` which are not supported here

file (instead, please specify files in sources)
col_select (instead, subset columns after dataset creation)
as_data_frame (instead, convert to data frame after dataset creation)
parse_options

Examples

# Set up directory for examples
tf <- tempfile()
dir.create(tf)
df <- data.frame(x = c("1", "2", "NULL"))

file_path <- file.path(tf, "file1.txt")
write.table(df, file_path, sep = ",", row.names = FALSE)

read_csv_arrow(file_path, na = c("", "NA", "NULL"), col_names = "y", skip = 1)
#> # A tibble: 3 x 1
#>       y
#>   <int>
#> 1     1
#> 2     2
#> 3    NA
open_csv_dataset(file_path, na = c("", "NA", "NULL"), col_names = "y", skip = 1)
#> FileSystemDataset with 1 csv file
#> y: int64

unlink(tf)

Open a multi-file dataset of CSV or other delimiter-separated format

Usage

Arguments

Options currently supported by read_delim_arrow() which are not supported here

See also

Examples

Options currently supported by `read_delim_arrow()` which are not supported here