R: Reads binary data from disjoint sections of a connection or a...

readBinFragments {R.utils} | R Documentation

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

### Description

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

### Usage

    ## Default S3 method:
    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 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.

### Value

Returns a `vector` of the requested `mode`().

### Author(s)

Henrik Bengtsson

### See Also

`writeBinFragments`().

### 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...\n")
    # 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\n")

    cat("Write file...\n")
    # 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\n")

    # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    # Ditto but via a connection
    # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    cat("Read connection...\n")
    # 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\n")

    # Update every 16:th byte in a connection
    cat("Write connection...\n")
    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\n")

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

[Package R.utils version 2.7.0 Index]