i_starmap: Iteror that applies a given function to the elements of an...

In iterors: Fast, Compact Iterators and Tools

Iteror that applies a given function to the elements of an iterable.

Description

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

Usage

i_starmap(f, x)

i_star(f, x)

Arguments

f	a function to apply to the elements of x
x	an iterable object

Details

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

The primary difference between i_starmap and i_map 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.

Value

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

Examples

pow <- function(x, y) {
  x^y
}
it <- i_starmap(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 <- i_starmap(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 <- i_starmap(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 <- i_starmap(sum, iris_x)
unlist(as.list(it4)) - rowSums(iris_x) < tolerance

iterors documentation built on May 31, 2023, 5:36 p.m.