Virtual R Types On Disk.
These functions describe the types of raw binary data stored on disk.
char(length = 0, nul = TRUE) uchar(length = 0) logi8(length = 0) logi32(length = 0) int8(length = 0) uint8(length = 0) int16(length = 0) uint16(length = 0) int24(length = 0) uint24(length = 0) int32(length = 0) int64(length = 0) real32(length = 0) real64(length = 0) cplx(length = 0) as.Ctype(x) is.Ctype(x)
length |
desired length. |
x |
R object to coerce or test |
nul |
are characters delimited by a nul byte? |
R has very limited storage types. There is one type of integer and one type of float (double). Storage to disk often can be made more efficient by reducing the precision of the data. These functions provide for a sort of virtual mapping from disk to native R type, for use with mmap-ed files.
When a memory mapping is created, a conversion method if declared for both extracting values from disk, as well as replacing elements on disk. The preceeding functions are used in the internal compiled code to handle the conversion.
It is the user's responsibility to ensure that data fits within the prescribed types.
An R typed vector of length ‘length’ with a virtual type and class ‘Ctype’. Additional information related to number of bytes and whether the vitrual type is signed is also contained.
The is no attempt to store or read metadata with respect to the extracted or replaced data. This is simply a low level interface to facilitate data reading and writing.
R vectors may be used to create files on disk
matching the specified type using the functions
writeBin with the appropriate size
argument. See also.
Jeffrey A. Ryan
tmp <- tempfile() # write a 1 byte signed integer -128:127 writeBin(-127:127L, tmp, size=1L) file.info(tmp)$size one_byte <- mmap(tmp, int8()) one_byte[] munmap(one_byte) # write a 1 byte unsigned integer 0:255 writeBin(0:255L, tmp, size=1L) file.info(tmp)$size one_byte <- mmap(tmp, uint8()) one_byte[] munmap(one_byte) # write a 2 byte integer -32768:32767 writeBin(c(-32768L,32767L), tmp, size=2L) file.info(tmp)$size two_byte <- mmap(tmp, int16()) two_byte[] munmap(two_byte) # write a 2 byte unsigned integer 0:65535 writeBin(c(0L,65535L), tmp, size=2L) two_byte <- mmap(tmp, uint16()) two_byte[] # replacement methods automatically (watch precision!!) two_byte[1] <- 50000 two_byte[] # values outside of range (above 65535 for uint16 will be wrong) two_byte[1] <- 65535 + 1 two_byte[] munmap(two_byte) # write a 4 byte integer standard R type writeBin(1:10L, tmp, size=4L) four_byte <- mmap(tmp, int32()) four_byte[] munmap(four_byte) # write 32 bit integers as 64 bit longs (where supported) int64() # note it is a double in R, but described as int64 writeBin(1:10L, tmp, size=8L) eight_byte <- mmap(tmp, int64()) storage.mode(eight_byte[]) # using R doubles to preserve most long values eight_byte[5] <- 2^40 # write as a long, a value in R that is double eight_byte[5] munmap(eight_byte) unlink(tmp)
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