#' Feature Transformation -- Discrete Cosine Transform (DCT) (Transformer)
#'
#' A feature transformer that takes the 1D discrete cosine transform of a real
#' vector. No zero padding is performed on the input vector. It returns a real
#' vector of the same length representing the DCT. The return vector is scaled
#' such that the transform matrix is unitary (aka scaled DCT-II).
#'
#' @template roxlate-ml-feature-input-output-col
#' @template roxlate-ml-feature-transformer
#'
#' @param inverse Indicates whether to perform the inverse DCT (TRUE) or forward DCT (FALSE).
#' @export
ft_dct <- function(x, input_col = NULL, output_col = NULL,
inverse = FALSE, uid = random_string("dct_"), ...) {
check_dots_used()
UseMethod("ft_dct")
}
ml_dct <- ft_dct
#' @export
ft_dct.spark_connection <- function(x, input_col = NULL, output_col = NULL,
inverse = FALSE, uid = random_string("dct_"), ...) {
.args <- list(
input_col = input_col,
output_col = output_col,
inverse = inverse,
uid = uid
) %>%
c(rlang::dots_list(...)) %>%
validator_ml_dct()
jobj <- spark_pipeline_stage(
x, "org.apache.spark.ml.feature.DCT",
input_col = .args[["input_col"]], output_col = .args[["output_col"]], uid = .args[["uid"]]
) %>%
invoke("setInverse", .args[["inverse"]])
new_ml_dct(jobj)
}
#' @export
ft_dct.ml_pipeline <- function(x, input_col = NULL, output_col = NULL,
inverse = FALSE, uid = random_string("dct_"), ...) {
transformer <- ft_dct.spark_connection(
x = spark_connection(x),
input_col = input_col,
output_col = output_col,
inverse = inverse,
uid = uid
)
ml_add_stage(x, transformer)
}
#' @export
ft_dct.tbl_spark <- function(x, input_col = NULL, output_col = NULL,
inverse = FALSE, uid = random_string("dct_"), ...) {
transformer <- ft_dct.spark_connection(
x = spark_connection(x),
input_col = input_col,
output_col = output_col,
inverse = inverse,
uid = uid
)
ml_transform(transformer, x)
}
new_ml_dct <- function(jobj) {
new_ml_transformer(jobj, class = "ml_dct")
}
#' @rdname ft_dct
#' @details \code{ft_discrete_cosine_transform()} is an alias for \code{ft_dct} for backwards compatibility.
#' @export
ft_discrete_cosine_transform <- function(x, input_col, output_col, inverse = FALSE, uid = random_string("dct_"), ...) {
UseMethod("ft_dct")
}
validator_ml_dct <- function(.args) {
.args <- validate_args_transformer(.args)
.args[["inverse"]] <- cast_scalar_logical(.args[["inverse"]])
.args
}
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