R/rowwise_table.R

In mlr3misc: Helper Functions for 'mlr3'

#' @title Row-Wise Constructor for 'data.table'
#'
#' @description
#' Similar to the \CRANpkg{tibble} function `tribble()`, this function
#' allows to construct tabular data in a row-wise fashion.
#'
#' The first arguments passed as formula will be interpreted as column names.
#' The remaining arguments will be put into the resulting table.
#'
#' @param ... (`any`)\cr
#'   Arguments: Column names in first rows as formulas (with empty left hand side),
#'   then the tabular data in the following rows.
#' @param .key (`character(1)`)\cr
#'   If not `NULL`, set the key via [data.table::setkeyv()] after constructing the
#'   table.
#'
#' @return [data.table::data.table()].
#' @export
#' @examples
#' rowwise_table(
#'   ~a, ~b,
#'   1, "a",
#'   2, "b"
#' )
rowwise_table = function(..., .key = NULL) {

  dots = list(...)

  for (i in seq_along(dots)) {
    if (!inherits(dots[[i]], "formula")) {
      ncol = i - 1L
      break
    }
  }

  if (ncol == 0L) {
    stop("No column names provided")
  }

  n = length(dots) - ncol
  if (n %% ncol != 0L) {
    stop("Data is not rectangular")
  }

  tab = lapply(seq_len(ncol), function(i) simplify2array(dots[seq(from = ncol + i, to = length(dots), by = ncol)]))
  tab = setnames(setDT(tab), map_chr(head(dots, ncol), function(x) attr(terms(x), "term.labels")))
  if (!is.null(.key)) {
    setkeyv(tab, .key)
  }
  tab
}