iterate: Apply a function repeatedly
In funprog: Functional Programming

Description Usage Arguments Details Value Examples

View source: R/iterate.R

Apply a function to a value, then reapply the same function to the result and so on... until a condition on the result is met (or a certain number of iterations reached).

1	iterate(x, f, stop_fun = NULL, stop_n = Inf, accumulate = FALSE)

`x`	initial value.
`f`	the function to apply.
`stop_fun`	a predicate (function) evaluated on the current result, which will stop the process if its result is `TRUE`. If not provided, the process will stop after `stop_n` iteration (see below).
`stop_n`	maximal number of times the function will be applied (mandatory if `stop_fun` is not defined).
`accumulate`	by default, the function returns only the last element. To get the list of all intermediate results, turn this parameter to `TRUE`.

As it is a very generic function (x can be any type of object) and the number of computations cannot be known in advance, iterate can be quite inefficient (particularly if you use accumulate = TRUE).

The last result, or the list of all results if accumulate = TRUE.

# https://en.wikipedia.org/wiki/Collatz_conjecture
syracuse <- function(x) if (x %% 2) 3 * x + 1 else x / 2
iterate(
  10,
  syracuse,
  stop_fun = function(n) n == 1,
  accumulate = TRUE
)

# https://en.wikipedia.org/wiki/H%C3%A9non_map
henon_attractor <-
  iterate(
    c(-1, 0.1),
    function(x) c(1 - 1.4 * x[1]^2 + x[2], 0.3 * x[1]),
    stop_n = 5000,
    accumulate = TRUE
  )
plot(
  sapply(henon_attractor, function(.) .[1]),
  sapply(henon_attractor, function(.) .[2]),
  pch = "."
)