readBinFragments
From R.utils v1.32.4
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, origin=c("current", "start"), 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 Nx2matrix
of N from-to index intervals specifying the elements to be read. Positions are either rela - origin
- A
character
string specify whether the indices in argumentidxs
are relative to the"start"
or the"current"
position of the file/connection. - 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 aVerbose
object.
Value
See Also
Examples
# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
# Create a data file
# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
data <- 1:255
size <- 2
pathname <- tempfile("exampleReadBinFragments")
writeBin(con=pathname, data, size=size)
# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
# Read and write using index vectors
# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
cat("Read file...
")
# 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)
# Read every 16:th byte in a connection starting with the 6th.
idxs <- idxs + 5L;
x <- readBinFragments(pathname, what="integer", size=size, signed=FALSE, idxs=idxs)
stopifnot(identical(x, data[idxs]))
print(x)
cat("Read file...done
")
cat("Write file...
")
# Update every 16:th byte in the file
idxs <- seq(from=1, to=255, by=16)
x0 <- data[idxs]
writeBinFragments(pathname, idxs=idxs, rev(x0), 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))
# Assert everything is as expected
# Read the complete file
x <- readBin(pathname, what="integer", size=size, signed=FALSE, n=length(data))
stopifnot(identical(x, data))
cat("Write file...done
")
# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
# Ditto but via a connection
# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
cat("Read connection...
")
# Read every 16:th byte in a connection
con <- file(pathname, open="rb")
idxs <- seq(from=1, to=255, by=16)
x <- readBinFragments(con, what="integer", size=size, signed=FALSE, idxs=idxs)
stopifnot(identical(x, data[idxs]))
print(x)
# Read every 16:th byte in a connection starting with the 6th.
idxs <- idxs + 5L;
x <- readBinFragments(con, what="integer", size=size, signed=FALSE, idxs=idxs, origin="start")
stopifnot(identical(x, data[idxs]))
print(x)
close(con)
cat("Read connection...done
")
# Update every 16:th byte in a connection
cat("Write connection...
")
con <- file(pathname, open="r+b")
idxs <- seq(from=1, to=255, by=16)
x0 <- data[idxs]
writeBinFragments(pathname, idxs=idxs, rev(x0), 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, origin="start")
print(x)
stopifnot(identical(x0, x))
close(con)
# Assert everything is as expected
# Read the complete file
x <- readBin(pathname, what="integer", size=size, signed=FALSE, n=length(data))
stopifnot(identical(x, data))
cat("Write connection...done
")
# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
# Clean up
# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
file.remove(pathname)
Community examples
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