itakewhile: Iterator that returns elements while a predicate function...
In itertools2: itertools2: Functions creating iterators for efficient looping

Description Usage Arguments Value Examples

Constructs an iterator that returns elements from an iterable object as long as the given predicate function returns TRUE.

1	itakewhile(predicate, object)

`predicate`	a function that determines whether an element is `TRUE` or `FALSE`. The function is assumed to take only one argument.
`object`	an iterable object

iterator object

# Filters out numbers exceeding 5
not_too_large <- function(x) {
  x <= 5
}
it <- itakewhile(not_too_large, 1:100)
unlist(as.list(it)) == 1:5

# Same approach but uses an anonymous function
it2 <- itakewhile(function(x) x <= 10, seq(2, 100, by=2))
unlist(as.list(it2)) == c(2, 4, 6, 8, 10)