| readBinFragments {R.utils} | R Documentation |
Reads binary data from disjoint sections of a connection or a file.
## Default S3 method: readBinFragments(con, what, idxs=1, size=NA, ..., verbose=FALSE)
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. |
Returns a vector of the requested mode().
Henrik Bengtsson (http://www.braju.com/R/)
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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)
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# Read and write using index vectors
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# 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))
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# Clean up
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file.remove(pathname)