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#' Linear combination filter
#'
#' `step_lincomb()` creates a *specification* of a recipe step that will
#' potentially remove numeric variables that have exact linear combinations
#' between them.
#'
#' @inheritParams step_center
#' @param max_steps The number of times to apply the algorithm.
#' @param removals A character string that contains the names of
#' columns that should be removed. These values are not determined
#' until [prep()] is called.
#' @template step-return
#' @template filter-steps
#' @family variable filter steps
#' @author Max Kuhn, Kirk Mettler, and Jed Wing
#' @export
#'
#' @details This step finds exact linear combinations between two
#' or more variables and recommends which column(s) should be
#' removed to resolve the issue. This algorithm may need to be
#' applied multiple times (as defined by `max_steps`).
#'
#' # Tidying
#'
#' When you [`tidy()`][tidy.recipe()] this step, a tibble is returned with
#' columns `terms` and `id`:
#'
#' \describe{
#' \item{terms}{character, the selectors or variables selected}
#' \item{id}{character, id of this step}
#' }
#'
#' @template case-weights-not-supported
#'
#' @examplesIf rlang::is_installed("modeldata")
#' data(biomass, package = "modeldata")
#'
#' biomass$new_1 <- with(
#' biomass,
#' .1 * carbon - .2 * hydrogen + .6 * sulfur
#' )
#' biomass$new_2 <- with(
#' biomass,
#' .5 * carbon - .2 * oxygen + .6 * nitrogen
#' )
#'
#' biomass_tr <- biomass[biomass$dataset == "Training", ]
#' biomass_te <- biomass[biomass$dataset == "Testing", ]
#'
#' rec <- recipe(HHV ~ carbon + hydrogen + oxygen + nitrogen +
#' sulfur + new_1 + new_2,
#' data = biomass_tr
#' )
#'
#' lincomb_filter <- rec %>%
#' step_lincomb(all_numeric_predictors())
#'
#' lincomb_filter_trained <- prep(lincomb_filter, training = biomass_tr)
#' lincomb_filter_trained
#'
#' tidy(lincomb_filter, number = 1)
#' tidy(lincomb_filter_trained, number = 1)
step_lincomb <-
function(recipe,
...,
role = NA,
trained = FALSE,
max_steps = 5,
removals = NULL,
skip = FALSE,
id = rand_id("lincomb")) {
add_step(
recipe,
step_lincomb_new(
terms = enquos(...),
role = role,
trained = trained,
max_steps = max_steps,
removals = removals,
skip = skip,
id = id
)
)
}
step_lincomb_new <-
function(terms, role, trained, max_steps, removals, skip, id) {
step(
subclass = "lincomb",
terms = terms,
role = role,
trained = trained,
max_steps = max_steps,
removals = removals,
skip = skip,
id = id
)
}
#' @export
prep.step_lincomb <- function(x, training, info = NULL, ...) {
col_names <- recipes_eval_select(x$terms, training, info)
check_type(training[, col_names], types = c("double", "integer"))
filter <- iter_lc_rm(
x = training[, col_names],
max_steps = x$max_steps
)
step_lincomb_new(
terms = x$terms,
role = x$role,
trained = TRUE,
max_steps = x$max_steps,
removals = filter,
skip = x$skip,
id = x$id
)
}
#' @export
bake.step_lincomb <- function(object, new_data, ...) {
new_data <- recipes_remove_cols(new_data, object)
new_data
}
#' @export
print.step_lincomb <-
function(x, width = max(20, options()$width - 36), ...) {
if (x$trained) {
title <- "Linear combination filter removed "
} else {
title <- "Linear combination filter on "
}
print_step(x$removals, x$terms, x$trained, title, width)
invisible(x)
}
recommend_rm <- function(x, eps = 1e-6, ...) {
if (!is.matrix(x)) {
x <- as.matrix(x)
}
qr_decomp <- qr(x)
qr_decomp_R <- qr.R(qr_decomp) # extract R matrix
num_cols <- ncol(qr_decomp_R) # number of columns in R
rank <- qr_decomp$rank # number of independent columns
pivot <- qr_decomp$pivot # get the pivot vector
if (is.null(num_cols) || rank == num_cols) {
rm_list <- character(0) # there are no linear combinations
} else {
p1 <- seq_len(rank)
X <- qr_decomp_R[p1, p1] # extract the independent columns
Y <- qr_decomp_R[p1, -p1, drop = FALSE] # extract the dependent columns
b <- qr(X) # factor the independent columns
b <- qr.coef(b, Y) # get regression coefficients of
# the dependent columns
b[abs(b) < eps] <- 0 # zap small values
# generate a list with one element for each dependent column
combos <- lapply(
seq_len(ncol(Y)),
function(i) {
c(pivot[rank + i], pivot[which(b[, i] != 0)])
}
)
rm_list <- unlist(lapply(combos, function(x) {
x[1]
}))
rm_list <- colnames(x)[rm_list]
}
rm_list
}
iter_lc_rm <- function(x,
max_steps = 10,
verbose = FALSE) {
if (ncol(x) == 0L) {
# Empty selection
return(character())
}
orig_names <- colnames(x)
if (!is.matrix(x)) {
x <- as.matrix(x)
}
# converting to matrix may alter column names
name_df <- data.frame(
orig = orig_names,
current = colnames(x),
stringsAsFactors = FALSE
)
for (i in seq_len(max_steps)) {
if (verbose) {
cat(i)
}
if (i == max_steps) {
break()
}
lcs <- recommend_rm(x)
if (length(lcs) == 0) {
break()
} else {
if (verbose) {
cat(" removing", length(lcs), "\n")
}
x <- x[, !(colnames(x) %in% lcs)]
}
}
if (verbose) {
cat("\n")
}
name_df <- name_df[!(name_df$current %in% colnames(x)), ]
name_df$orig
}
#' @rdname tidy.recipe
#' @export
tidy.step_lincomb <- tidy_filter
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