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#' Filter rows by position using dplyr
#'
#' `step_slice` creates a *specification* of a recipe step
#' that will filter rows using [dplyr::slice()].
#'
#' @template row-ops
#' @inheritParams step_center
#' @param ... Integer row values. See
#' [dplyr::slice()] for more details. For the `tidy`
#' method, these are not currently used.
#' @param role Not used by this step since no new variables are
#' created.
#' @param inputs Quosure of values given by `...`.
#' @param skip A logical. Should the step be skipped when the
#' recipe is baked by [bake.recipe()]? While all operations are baked
#' when [prep.recipe()] is run, some operations may not be able to be
#' conducted on new data (e.g. processing the outcome variable(s)).
#' Care should be taken when using `skip = FALSE`.
#' @return An updated version of `recipe` with the new step
#' added to the sequence of existing steps (if any). For the
#' `tidy` method, a tibble with columns `terms` which
#' contains the filtering indices.
#' @details When an object in the user's global environment is
#' referenced in the expression defining the new variable(s),
#' it is a good idea to use quasiquotation (e.g. `!!`)
#' to embed the value of the object in the expression (to
#' be portable between sessions). See the examples.
#' @keywords datagen
#' @concept preprocessing
#' @export
#' @examples
#' rec <- recipe( ~ ., data = iris) %>%
#' step_slice(1:3)
#'
#' prepped <- prep(rec, training = iris %>% slice(1:75))
#' tidy(prepped, number = 1)
#'
#' library(dplyr)
#'
#' dplyr_train <-
#' iris %>%
#' as_tibble() %>%
#' slice(1:75) %>%
#' slice(1:3)
#'
#' rec_train <- bake(prepped, new_data = NULL)
#' all.equal(dplyr_train, rec_train)
#'
#' dplyr_test <-
#' iris %>%
#' as_tibble() %>%
#' slice(76:150) %>%
#' slice(1:3)
#' rec_test <- bake(prepped, iris %>% slice(76:150))
#' all.equal(dplyr_test, rec_test)
#'
#' # Embedding the integer expression (or vector) into the
#' # recipe:
#'
#' keep_rows <- 1:6
#'
#' qq_rec <-
#' recipe( ~ ., data = iris) %>%
#' # Embed `keep_rows` in the call using !!
#' step_slice(!!keep_rows) %>%
#' prep(training = iris)
#'
#' tidy(qq_rec, number = 1)
#' @seealso [step_filter()] [step_naomit()] [step_sample()]
step_slice <- function(
recipe, ...,
role = NA,
trained = FALSE,
inputs = NULL,
skip = TRUE,
id = rand_id("slice")
) {
inputs <- enquos(...)
add_step(
recipe,
step_slice_new(
terms = terms,
trained = trained,
role = role,
inputs = inputs,
skip = skip,
id = id
)
)
}
step_slice_new <-
function(terms, role, trained, inputs, skip, id) {
step(
subclass = "slice",
terms = terms,
role = role,
trained = trained,
inputs = inputs,
skip = skip,
id = id
)
}
#' @export
prep.step_slice <- function(x, training, info = NULL, ...) {
step_slice_new(
terms = x$terms,
trained = TRUE,
role = x$role,
inputs = x$inputs,
skip = x$skip,
id = x$id
)
}
#' @export
bake.step_slice <- function(object, new_data, ...) {
dplyr::slice(new_data, !!!object$inputs)
}
print.step_slice <-
function(x, width = max(20, options()$width - 35), ...) {
cat("Row filtering via position")
if (x$trained) {
cat(" [trained]\n")
} else {
cat("\n")
}
invisible(x)
}
#' @rdname step_slice
#' @param x A `step_slice` object
#' @export
tidy.step_slice <- function(x, ...) {
cond_expr <- map(x$inputs, quo_get_expr)
cond_expr <- map_chr(cond_expr, quo_text, width = options()$width, nlines = 1)
tibble(
terms = cond_expr,
id = rep(x$id, length(x$inputs))
)
}
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