itertools2 (version 0.1.1)

istarmap: Iterator that applies a given function to the elements of an iterable.

Description

Constructs an iterator that applies the function f concurrently to the elements within the list x.

Usage

istarmap(f, x)
istar(f, x)

Arguments

f

a function to apply to the elements of x

x

an iterable object

Value

iterator that returns the values of object along with the index of the object.

Details

The iterator returned is exhausted when the shortest element in x is exhausted. Note that istarmap does not recycle arguments as Map does.

The primary difference between istarmap and imap is that the former expects an iterable object whose elements are already grouped together, while the latter case groups the arguments together before applying the given function. The choice is a matter of style and convenience.

Examples

pow <- function(x, y) {
  x^y
}
it <- istarmap(pow, list(c(2, 3, 10), c(5, 2, 3)))
unlist(as.list(it)) == c(32, 9, 1000)

# Similar to the above, but because the second vector is exhausted after two
# calls to `nextElem`, the iterator is exhausted.
it2 <- istarmap(pow, list(c(2, 3, 10), c(5, 2)))
unlist(as.list(it2)) == c(32, 9)

# Another similar example but with lists instead of vectors
it3 <- istarmap(pow, list(list(2, 3, 10), list(5, 2, 3)))
as.list(it3)

# Computes sum of each row in the iris data set
# Numerically equivalent to base::rowSums()
tolerance <- sqrt(.Machine$double.eps)
iris_x <- iris[, -5]
it4 <- istarmap(sum, iris_x)
unlist(as.list(it4)) - rowSums(iris_x) < tolerance