read_lines: Read/write lines to/from a file

Description

read_lines() reads up to n_max lines from a file. New lines are not included in the output. read_lines_raw() produces a list of raw vectors, and is useful for handling data with unknown encoding. write_lines() takes a character vector or list of raw vectors, appending a new line after each entry.

Usage

read_lines(
  file,
  skip = 0,
  skip_empty_rows = FALSE,
  n_max = Inf,
  locale = default_locale(),
  na = character(),
  lazy = should_read_lazy(),
  num_threads = readr_threads(),
  progress = show_progress()
)
read_lines_raw(
  file,
  skip = 0,
  n_max = -1L,
  num_threads = readr_threads(),
  progress = show_progress()
)
write_lines(
  x,
  file,
  sep = "\n",
  na = "NA",
  append = FALSE,
  num_threads = readr_threads(),
  path = deprecated()
)

Value

read_lines(): A character vector with one element for each line. read_lines_raw(): A list containing a raw vector for each line.

write_lines() returns x, invisibly.

Arguments

file

Either a path to a file, a connection, or literal data (either a single string or a raw vector).

Files ending in .gz, .bz2, .xz, or .zip will be automatically uncompressed. Files starting with http://, https://, ftp://, or ftps:// will be automatically downloaded. Remote gz files can also be automatically downloaded and decompressed.

Literal data is most useful for examples and tests. To be recognised as literal data, the input must be either wrapped with I(), be a string containing at least one new line, or be a vector containing at least one string with a new line.

Using a value of clipboard() will read from the system clipboard.

skip

Number of lines to skip before reading data.

skip_empty_rows

Should blank rows be ignored altogether? i.e. If this option is TRUE then blank rows will not be represented at all. If it is FALSE then they will be represented by NA values in all the columns.

n_max

Number of lines to read. If n_max is -1, all lines in file will be read.

locale

The locale controls defaults that vary from place to place. The default locale is US-centric (like R), but you can use locale() to create your own locale that controls things like the default time zone, encoding, decimal mark, big mark, and day/month names.

na

Character vector of strings to interpret as missing values. Set this option to character() to indicate no missing values.

lazy

Read values lazily? By default, this is FALSE, because there are special considerations when reading a file lazily that have tripped up some users. Specifically, things get tricky when reading and then writing back into the same file. But, in general, lazy reading (lazy = TRUE) has many benefits, especially for interactive use and when your downstream work only involves a subset of the rows or columns.

Learn more in should_read_lazy() and in the documentation for the altrep argument of vroom::vroom().

num_threads

The number of processing threads to use for initial parsing and lazy reading of data. If your data contains newlines within fields the parser should automatically detect this and fall back to using one thread only. However if you know your file has newlines within quoted fields it is safest to set num_threads = 1 explicitly.

progress

Display a progress bar? By default it will only display in an interactive session and not while knitting a document. The automatic progress bar can be disabled by setting option readr.show_progress to FALSE.

x

A character vector or list of raw vectors to write to disk.

sep

The line separator. Defaults to \\n, commonly used on POSIX systems like macOS and linux. For native windows (CRLF) separators use \\r\\n.

append

If FALSE, will overwrite existing file. If TRUE, will append to existing file. In both cases, if the file does not exist a new file is created.

path

Use the file argument instead.

Examples

Run this code

read_lines(file.path(R.home("doc"), "AUTHORS"), n_max = 10)
read_lines_raw(file.path(R.home("doc"), "AUTHORS"), n_max = 10)

tmp <- tempfile()

write_lines(rownames(mtcars), tmp)
read_lines(tmp, lazy = FALSE)
read_file(tmp) # note trailing \n

write_lines(airquality$Ozone, tmp, na = "-1")
read_lines(tmp)

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