getZipInfo: Read table of contents from zip archive

In omegahat/Rcompression: In-memory decompression for GNU zip and bzip2 formats

Read table of contents from zip archive

Description

This function reads the specified zip file and returns information about each file contained in the archive. This can be useful when one wants to find out what files are in an archive without unzipping the file or reading the contents via a call to the system zip command, e.g. zip -l, and parsing the results. All the manipulations are done in memory and require no disk access. This can be returned as a list with an object for each file, or as a data frame with a row for each element.

Usage

getZipInfo(filename, asDataFrame = TRUE, filename.size = 1024,
            comment = TRUE)

Arguments

filename	the name of the zip file. This can contain ~ which is expanded using path.expand.
asDataFrame	a logical value indicating whether to convert the simple list of information objects to a rectangular table. This involves a non-trivial number of computations at present (unoptimized!) and so it may wise to avoid this for very large zip files if one is interested in a single field.
filename.size	the number of bytes to use for the string used as the work space for the file names in the archive. This allows the user to enlarge the work space for archives with very long file names, including the directories.
comment	a logical value controlling whether the comments should be retrieved (TRUE for retrieve).

Details

This uses the code from the minizip directory in the zlib distribution. The code was created and is copyrighted by Gilles Volant. There were some minor changes to ANSI'fy the C code routine definitions to make it accesible to a C++ compiler. This was needed so as to be able to automate the code that interfaced to the native routines and data structures using the RGCCTranslationUnit package from the omegahat.org Web site.

Value

If asDataFrame is TRUE, a data frame with 15 columns. These corrspond to the fields of the unz_file_info-class class.

If asDataFrame is FALSE, the return value is a named list containing the unz_file_info-class objects

Note

This code builds on the internal functions that are automatically generated using RGCCTranslationUnit

Author(s)

Duncan Temple Lang

References

http://www.gzip.org/zlib/ zlib

See Also

connections

Examples

  zipFile = system.file("sampleData", "MyZip.zip", package = "Rcompression")
  df = getZipInfo(zipFile)
  df[grep("^R/", rownames(df)), ]
  weekdays(df$date)


  # Treating the files element-wise rather than in a data frame.
  els = getZipInfo(zipFile, FALSE)
  sapply(els, slot, "compressed_size")/sapply(els, slot, "uncompressed_size")

   # Get the month the file was last modified.
   # This is in the tmu_date slot of each element.
  sapply(els, function(x) x@tmu_date@tm_mon)

omegahat/Rcompression documentation built on Nov. 29, 2023, 12:45 a.m.