memCompress(base)
memCompress()所属R语言包：base
In-memory Compression and Decompression
内存中的压缩和减压
译者：生物统计家园网 机器人LoveR
描述----------Description----------
In-memory compression or decompression for raw vectors.
内存中压缩或解压缩的原始向量。
用法----------Usage----------
memCompress(from, type = c("gzip", "bzip2", "xz", "none"))
memDecompress(from,
type = c("unknown", "gzip", "bzip2", "xz", "none"),
asChar = FALSE)
参数----------Arguments----------
参数：from
A raw vector. For memCompress a character vector will be converted to a raw vector with character strings separated by "\n".
原始向量。 memCompress由"\n"分隔的字符串将被转换成一个字符向量与原始向量。
参数：type
character string, the type of compression. May be abbreviated to a single letter, defaults to the first of the alternatives.
字符串，压缩类型。可能是缩写为一个字母，默认的替代品第一。
参数：asChar
logical: should the result be converted to a character string?
逻辑：结果被转换为一个字符串？
Details
详情----------Details----------
type = "none" passes the input through unchanged, but may be useful if type is a variable.
type = "none"通过不变的投入，但可能是有用的，如果type是一个变量。
type = "unknown" attempts to detect the type of compression applied (if any): this will always succeed for bzip2 compression, and will succeed for other forms if there is a suitable header. It will auto-detect the "magic" header ("\x1f\x8b") added to files by the gzip program (and to files written by gzfile), but memCompress does not add such a header.
type = "unknown"试图检测压缩应用类型（如有）：这将总是成功，bzip2压缩和其他形式的成功，如果有一个合适的标题。它会自动检测魔头（"\x1f\x8b"）gzip方案的文件（和），但gzfile不memCompress书面文件添加到添加这样一个头。
bzip2 compression always adds a header ("BZh").
bzip2压缩总是增加了一个头（"BZh"）。
Compressing with type = "xz" is equivalent to compressing a file with xz -9e (including adding the "magic" header): decompression should cope with the contents of any file compressed with xz version 4.999 and some versions of lzma. There are other versions, in particular "raw" streams, that are not currently handled.
type = "xz"压缩相当于压缩文件xz -9e（包括加入“神奇”的头）：xz4.999版本和一些压缩的任何文件内容应配合减压版本lzma。有其他版本，在特定的“原始”流，是目前尚未处理。
All the types of compression can expand the input: for "gzip" and "bzip" the maximum expansion is known and so memCompress can always allocate sufficient space. For "xz" it is possible (but extremely unlikely) that compression will fail if the output would have been too large.
所有的压缩类型，可扩展输入："gzip"和"bzip"最大的扩张是已知的，所以memCompress总是可以分配足够的空间。 "xz"它是可能的（但极不可能），将失败，如果输出已经过大压缩。
值----------Value----------
A raw vector or a character string (if asChar = TRUE).
如果asChar = TRUE一个原始向量或字符串（）。
参见----------See Also----------
connections.
连接。
http://en.wikipedia.org/wiki/Data_compression for background on data compression, http://zlib.net/, http://en.wikipedia.org/wiki/Gzip, http://www.bzip.org/, http://en.wikipedia.org/wiki/Bzip2, http://tukaani.org/xz/ and http://en.wikipedia.org/wiki/Xz for references about the particular schemes used.
为背景，对数据压缩，http://zlib.net/，http://en.wikipedia.org/wiki/Gzip，http://www.bzip http://en.wikipedia.org/wiki/Data_compression。 ORG / http://en.wikipedia.org/wiki/Bzip2，http://tukaani.org/xz/和http://en.wikipedia.org/wiki/Xz参考使用的特别计划。
举例----------Examples----------
txt <- readLines(file.path(R.home("doc"), "COPYING"))
sum(nchar(txt))
txt.gz <- memCompress(txt, "g")
length(txt.gz)
txt2 <- strsplit(memDecompress(txt.gz, "g", asChar = TRUE), "\n")[[1]]
stopifnot(identical(txt, txt2))
txt.bz2 <- memCompress(txt, "b")
length(txt.bz2)
## can auto-detect bzip2:[＃可自动检测的bzip2：]
txt3 <- strsplit(memDecompress(txt.bz2, asChar = TRUE), "\n")[[1]]
stopifnot(identical(txt, txt3))
## xz compression is only worthwhile for large objects[＃XZ压缩是唯一值得大对象]
txt.xz <- memCompress(txt, "x")
length(txt.xz)
txt3 <- strsplit(memDecompress(txt.xz, asChar = TRUE), "\n")[[1]]
stopifnot(identical(txt, txt3))
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注：
注1：为了方便大家学习，本文档为生物统计家园网机器人LoveR翻译而成，仅供个人R语言学习参考使用，生物统计家园保留版权。
注2：由于是机器人自动翻译，难免有不准确之处，使用时仔细对照中、英文内容进行反复理解，可以帮助R语言的学习。
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发表于 2012-2-16 18:50:41
