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library(iterators)
# return an iterator that returns subvectors of a vector.
# can specify either "chunks" or "chunkSize" arguments
# since that is what the "idiv" function supports.
ivector <- function(x, ...) {
# don't evaluate x if is specified using the ':' operator
q <- substitute(x)
if (identical(q[[1]], as.name(':'))) {
rm(list='x') # being paranoid: don't want to evaluate promise
lower <- as.integer(eval.parent(q[[2]]))
upper <- as.integer(eval.parent(q[[3]]))
inc <- if (upper >= lower) 1L else -1L
len <- abs(upper - lower) + 1L
it <- idiv(len, ...)
nextEl <- function() {
n <- nextElem(it)
y <- seq(lower, by=inc, length=n)
lower <<- lower + (inc * n)
y
}
} else {
i <- 1
it <- idiv(length(x), ...)
nextEl <- function() {
n <- nextElem(it)
ix <- seq(i, length=n)
i <<- i + n
x[ix]
}
}
obj <- list(nextElem=nextEl)
class(obj) <- c('ivector', 'abstractiter', 'iter')
obj
}
# create a vector iterator that returns three subvectors
it <- ivector(1:25, chunks=3)
print(as.list(it))
# create a vector iterator that returns subvectors
# with a maximum length of 10
it <- ivector(25:1, chunkSize=10)
print(as.list(it))
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