readBinFragments

From R.utils v1.4.2 by Henrik Bengtsson

Reads binary data from disjoint sections of a connection or a file

Reads binary data from disjoint sections of a connection or a file.

Keywords: IO

Usage

## S3 method for class 'default':
readBinFragments(con, what, idxs=1, size=NA, ..., verbose=FALSE)

Arguments

con: A connection or the pathname of an existing file.
what: A character string or an object specifying the the data type (mode()) to be read.
idxs: A vector of (non-duplicated) indices or a Nx2 matrix of N from-to index intervals specifying the elements to be read.
size: The size of the data type to be read. If NA, the natural size of the data type is used.
...: Additional arguments passed to readBin().
verbose: A logical or a Verbose object.

Value

Returns a vector of the requested mode().

Examples

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# Create a data file
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data <- 1:255
size <- 2
pathname <- tempfile("exampleReadBinFragments")
writeBin(con=pathname, data, size=size)


# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
# Read and write using index vectors
# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
# Read every 16:th byte in the file
idxs <- seq(from=1, to=255, by=16)
x <- readBinFragments(pathname, what="integer", size=size, signed=FALSE, idxs=idxs)
stopifnot(identical(x, data[idxs]))
print(x)

# Update every 16:th byte in the file
x0 <- x
idxs <- seq(from=1, to=255, by=16)
writeBinFragments(pathname, idxs=idxs, rev(x), size=size)
x <- readBinFragments(pathname, what="integer", size=size, signed=FALSE, idxs=idxs)
print(x)
stopifnot(identical(rev(x0), x))

# Update every 16:th byte in the file
idxs <- seq(from=1, to=255, by=16)
writeBinFragments(pathname, idxs=idxs, rev(x), size=size)
x <- readBinFragments(pathname, what="integer", size=size, signed=FALSE, idxs=idxs)
print(x)
stopifnot(identical(x0, x))

# Read the complete file
x <- readBin(pathname, what="integer", size=size, signed=FALSE, n=length(data))
stopifnot(identical(x, data))


# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
# Clean up
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file.remove(pathname)

Documentation reproduced from package R.utils, version 1.4.2, License: LGPL (>= 2.1)

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