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

Usage

## S3 method for class 'default}(con, what, idxs=1, origin=c("current", "start"), size=NA, ..., verbose=FALSE)':
readBinFragmentsundefined

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

 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.
     Positions are either relative to the start or the current location
     of the file/connection as given by argument origin.}
   origin{A character string specify whether the indices
    in argument idxs 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 a Verbose object.}

 Returns a vector of the requested mode().

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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
# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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
")


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

 [object Object]

 writeBinFragments().


IO
Usage

Arguments
