Preview a Delimited Text File

Read the first n data rows of a delimited text file and return the result as a base R data.frame (a kind of head() for files).

Usage

peekFile(file, n = 10, ..., output = c("data.frame", "tibble"))

Arguments

file

character string specifying the file name.

n

integer specifying the number of data rows to read, defaults to 10.

...

additional arguments passed to readr::read_delim(), e.g. delim or skip. The arguments n_max and show_col_types are managed internally and will be ignored if supplied; guess_max defaults to n but may be overridden.

output

character, either "data.frame" (default) or "tibble", determining the class of the returned object. Conversion to data.frame is done by toBaseR(). The argument can be abbreviated. Note that it must be given as a named argument, as it follows the dots.

Value

a data.frame or a tibble (according to output) containing the first n data rows of the file.

Details

This function is intended for quickly inspecting large text files, including compressed files supported by readr::read_delim().

Column types are guessed from the previewed rows only (the default guess_max equals n). If early rows are not representative, supply a larger guess_max via the dots.

See also

readr::read_delim(), toBaseR(), head(),

Other file.io: parseSASDatalines(), pdfManual(), readDownload()

Examples

# a small file to look into
fn <- tempfile(fileext = ".csv")
write.csv(iris, fn, row.names = FALSE)

if (requireNamespace("readr", quietly = TRUE)) {

  peekFile(fn, delim = ",")

  # unrepresentative early rows: guess types over more lines
  peekFile(fn, n = 5, delim = ",", guess_max = 150)
}
#>   Sepal.Length Sepal.Width Petal.Length Petal.Width Species
#> 1          5.1         3.5          1.4         0.2  setosa
#> 2          4.9         3.0          1.4         0.2  setosa
#> 3          4.7         3.2          1.3         0.2  setosa
#> 4          4.6         3.1          1.5         0.2  setosa
#> 5          5.0         3.6          1.4         0.2  setosa

unlink(fn)