R/calc_isi.R

In jcpsantiago/gmi: Calculate Various Glucose Metabolism Indices

#' Calculate insulin-sensitivity index
#'
#' @param glu  An ordered vector of glucose values.
#' @param ins  An ordered vector of insulin values.
#' @param nefa An ordered vector of NEFA values.
#' @param bmi  Body-mass index.
#' @param body_weight Body weight in kg.
#' @param index Insulin sensitivity index as a string. This can be one of
#'     "Cederholm", "Gutt" (aka "ISI 0,120"), "Matsuda", "NEFA-ISI",
#'     "Stumvoll-ISI" or "Stumvoll-MCR".
#'
#' @return A double.
#' @export
#'
#' @examples
calc_isi <- function(glu = NULL, ins = NULL, nefa = NULL,
                     bmi = NULL, body_weight = NULL, index = NULL) {

  ## only these indexes are currently implemented
  allowed_indexes <- c(
    "FIRI", "HOMA-IR", "QUICKI", "QUICKI-R",
    "Cederholm", "Gutt", "Matsuda", "NEFA-ISI",
    "Stumvoll-ISI", "Stumvoll-MCR"
  )

  if (length(index) > 1) {
    stop("Don't be greedy! Only one index per function call, please")
  }

  if (!(index %in% allowed_indexes)) {
    stop(index, " is not a valid index, or not yet implemented")
  }

  if (length(bmi) > 1) {
    warning("Only the first value of bmi was used!")
  }

  if (length(body_weight) > 1) {
    warning("Only the first value of body_weight was used!")
  }


  ## some variables need to be numeric, or NULL if the index doesn't need it
  stopifnot(is_numeric_or_null(glu, ins, nefa, bmi, body_weight))


  switch(
    index,
    ## fasting-based
    FIRI = firi_index(glu, ins),
    `HOMA-IR` = homa_ir_index(glu, ins),
    QUICKI = quicki_index(glu, ins),
    `QUICKI-R` = revised_quicki_index(glu, ins, nefa),
    ## ogtt-based
    Cederholm = cederholm_index(glu, ins, body_weight),
    Gutt = gutt_index(glu, ins, body_weight),
    `ISSI-2` = beta_cell_fun_index(glu, ins),
    Matsuda = matsuda_index(glu, ins),
    `NEFA-ISI` = nefa_index(ins, bmi, nefa),
    `Stumvoll-ISI` = stumvoll_isi_index(glu, ins, bmi),
    `Stumvoll-MCR` = stumvoll_mcr_index(glu, ins, bmi)
  )
}