R/while_pipe.R

In MyKo101/mpipe: Adds extra functionality to pipelines

#' @name while_pipe
#'
#' @title
#' Perform an while-like loop in a pipeline
#'
#' @description
#' Allows the user to perform a while-like
#' loop without breaking out of a pipeline.
#' To maintain the flow of a pipeline, it is recommended
#' to use [`fseq`][] style arguments (i.e. pipelines) for the
#' `fun` argument.
#'
#' Within the `while_pipe()`, users can use the `.counter` variable
#' to reference how many iterations have been performed so far.
#'
#' @param data
#' the data being passed through the pipeline.
#'
#' @param cond
#' an expression to be evaluated in the context of `data` to
#' decide whether to perform `fun`. Should evaluate to a single
#' logical value or be coercible to one.
#'
#' @param fun
#' pipeline to perform until `cond` is `FALSE`.
#'
#'
#' @export
#'
#' @examples
#'
#' sample(100, 1) %>%
#'   runif() %>%
#'   pipe_cat("Current length: ", length(.), "\n") %>%
#'   while_pipe(
#'     length(.) > 1,
#'     . %>%
#'       diff() %>%
#'       magrittr::divide_by(2)
#'   )
#'
#'
#' tibble::tibble(x = runif(5)) %>%
#'   while_pipe(
#'     .counter <= 5,
#'     . %>%
#'       dplyr::mutate(!!paste0("x_", .counter) := x - x[.counter])
#'   )
while_pipe <- function(data, cond, fun) {
  c_env <- rlang::current_env()

  quo_cond <- enquo(cond)
  quo_cond <- rlang::quo_set_env(quo_cond, c_env)

  .counter <- 1L
  current_data <- data

  cond_eval <- eval_expr(current_data, !!quo_cond, .counter)


  new_fun <- copy_fun(fun)

  fun_var_env(new_fun, ".counter", .counter)

  while (cond_eval) {
    fun_var_env(new_fun, ".counter", .counter)
    current_data <- new_fun(current_data)

    .counter <- .counter + 1L
    cond_eval <- eval_expr(current_data, !!quo_cond, .counter)
  }

  current_data
}