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