gappyIndex {oce}

Create a Possibly Gappy Indexing Vector

Description

This is used internally to construct indexing arrays, mainly for adv and adp functions, in which readBin() is used to access isolated regions within a raw vector. The work is done in C++, for speed. Since this function is designed for use within oce, it does not offer many safeguards on the parameters, beyond detecting an overlapping situation that would occur if length exceeded the space between starts elements. Also, users ought to be aware that the behaviour of gappyIndex() might change at any time; simply stated, it is not intended for direct use except by the package developers.

Usage

gappyIndex(starts, offset = 0L, length = 4L)

Arguments

starts

integer vector of one or more values.

offset

integer value indicating the value to be added to each of the starts value, as the beginning of the sequence.

length

integer value indicating the number of elements of that sequence.

Details

For example, suppose data elements in a buffer named buf start at bytes 1000 and 2000, and that the goal is to skip the first 4 bytes of each of these sequences, and then to read the next 2 bytes as an unsigned 16-bit integer. This could be accomplished as follows.

library(oce)
buf <- readBin("filename", "raw", n=5000, size=1)
i <- gappyIndex(c(1000, 2000, 3000), 4, 2)
# i is 1004,1005, 2004,2005, 3004,3005
values <- readBin(buf[i], "integer", size=2, n=3, endian="little")

Author(s)

Dan Kelley