R: Read and Write Data in DCF Format

dcf {base}

R Documentation

Read and Write Data in DCF Format

Description

Reads or writes an R object from/to a file in Debian Control File format.

Usage

read.dcf(file, fields = NULL, all = FALSE)

write.dcf(x, file = "", append = FALSE,
          indent = 0.1 * getOption("width"),
          width = 0.9 * getOption("width"))

Arguments

`file`	either a character string naming a file or a connection. `""` indicates output to the console. For `read.dcf` this can name a `gzip`-compressed file.
`fields`	Fields to read from the DCF file. Default is to read all fields.
`all`	a logical indicating whether in case of multiple occurrences of a field in a record, all these should be gathered. If `all` is false (default), only the last such occurrence is used.
`x`	the object to be written, typically a data frame. If not, it is attempted to coerce `x` to a data frame.
`append`	logical. If `TRUE`, the output is appended to the file. If `FALSE`, any existing file of the name is destroyed.
`indent`	a positive integer specifying the indentation for continuation lines in output entries.
`width`	a positive integer giving the target column for wrapping lines in the output.

Details

DCF is a simple format for storing databases in plain text files that can easily be directly read and written by humans. DCF is used in various places to store R system information, like descriptions and contents of packages.

The DCF rules as implemented in R are:

A database consists of one or more records, each with one or more named fields. Not every record must contain each field. Fields may appear more than once in a record.
Regular lines start with a non-whitespace character.
Regular lines are of form tag:value, i.e., have a name tag and a value for the field, separated by : (only the first : counts). The value can be empty (=whitespace only).
Lines starting with whitespace are continuation lines (to the preceding field) if at least one character in the line is non-whitespace. Continuation lines where the only non-whitespace character is a . are taken as blank lines (allowing for multi-paragraph field values).
Records are separated by one or more empty (=whitespace only) lines.

By default, read.dcf returns a character matrix with one row per record and one column per field. Leading and trailing whitespace of field values is ignored. If a tag name is specified, but the corresponding value is empty, then an empty string is returned. If the tag name of a field is never used in a record, then NA is returned. If fields are repeated within a record, the last one encountered is returned. Malformed lines lead to an error. If all is true, a data frame is returned, again with one row per record and one column per field, and columns lists of character vectors for fields with multiple occurrences, and character vectors otherwise.

write.dcf does not write NA fields.

Examples

## Create a reduced version of the 'CONTENTS' file in package 'splines'
x <- read.dcf(file = system.file("CONTENTS", package = "splines"),
              fields = c("Entry", "Description"))
write.dcf(x)