R/bmi.R

In gipso/scaler: Tools to Process Health Measurement Scales

# https://iris.who.int/handle/10665/42330
# https://doi.org/10.1016/S0140-6736(03)15268-3

bmi <- function(weight, height, number = TRUE, cat = FALSE) {
  prettycheck:::assert_number(weight, lower = 20)
  prettycheck:::assert_number(height, lower = 0.5, upper = 3)
  prettycheck:::assert_flag(number)
  prettycheck:::assert_flag(cat)

  if (isFALSE(number) && isFALSE(cat)) {
    cli::cli_abort(paste0(
      "{.strong number} and {.strong cat} cannot both be ",
      "{.strong {cli::col_red('FALSE')}}."
    ))
  }

  if (isTRUE(number) && isTRUE(cat)) {
    cli::cli_abort(paste0(
      "{.strong number} and {.strong cat} cannot both be ",
      "{.strong {cli::col_red('TRUE')}}."
    ))
  }

  bmi_number <- weight / (height ** 2)

  if (isTRUE(number)) {
    bmi_number
  } else if (isTRUE(cat)) {
    if (bmi_number < 18.5) {
      bmi_cat <- "Underweight"
    } else if (bmi_number >= 18.5 && bmi_number < 25) {
      bmi_cat <- "Normal"
    } else if (bmi_number >= 25 && bmi_number < 30) {
      bmi_cat <- "Preobese"
    } else if (bmi_number >= 30 && bmi_number < 35) {
      bmi_cat <- "Obesity class 1"
    } else if (bmi_number >= 35 && bmi_number < 40) {
      bmi_cat <- "Obesity class 2"
    } else if (bmi_number >= 40) {
      bmi_cat <- "Obesity class 3"
    }

    paste0("~", round(bmi_number, 3), " (", bmi_cat, ")")
  }
}