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Read lines from a file

Source: R/vroom_lines.R
vroom_lines.Rd

vroom_lines() is similar to readLines(), however it reads the lines lazily like vroom(), so operations like length(), head(), tail() and sample() can be done much more efficiently without reading all the data into R.

Usage

vroom_lines(
  file,
  n_max = Inf,
  skip = 0,
  na = character(),
  skip_empty_rows = FALSE,
  locale = default_locale(),
  altrep = TRUE,
  altrep_opts = deprecated(),
  num_threads = vroom_threads(),
  progress = vroom_progress()
)

Arguments

file

Either a path to a file, a connection, or literal data (either a single string or a raw vector). file can also be a character vector containing multiple filepaths or a list containing multiple connections.

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, wrap the input with I().

n_max

Maximum number of lines to read.

skip

Number of lines to skip before reading data. If comment is supplied any commented lines are ignored after skipping.

na

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

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.

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.

altrep

Control which column types use Altrep representations, either a character vector of types, TRUE or FALSE. See vroom_altrep() for for full details.

altrep_opts

[Deprecated]

num_threads

Number of threads to use when reading and materializing vectors. If your data contains newlines within fields the parser will automatically be forced to use a single thread only.

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.

Examples

lines <- vroom_lines(vroom_example("mtcars.csv"))

length(lines)
#> [1] 33
head(lines, n = 2)
#> [1] "model,mpg,cyl,disp,hp,drat,wt,qsec,vs,am,gear,carb"
#> [2] "Mazda RX4,21,6,160,110,3.9,2.62,16.46,0,1,4,4"     
tail(lines, n = 2)
#> [1] "Maserati Bora,15,8,301,335,3.54,3.57,14.6,0,1,5,8"
#> [2] "Volvo 142E,21.4,4,121,109,4.11,2.78,18.6,1,1,4,2" 
sample(lines, size = 2)
#> [1] "AMC Javelin,15.2,8,304,150,3.15,3.435,17.3,0,0,3,2"       
#> [2] "Chrysler Imperial,14.7,8,440,230,3.23,5.345,17.42,0,0,3,4"