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")