R/convert.R

Defines functions get_conversion_table is_supported_unit convert

Documented in convert get_conversion_table

#' @title Convert from one unit type to another
#'
#' @description
#' Converts numeric vectors from one unit to another Approximately 1500 units
#' are available.
#' \code{\link{convert_gadget}} can help you build valid \code{convert()} expressions and
#' \code{\link{explore_units}} provides an interface for exploring the \code{\link{conversion_table}}
#' which underlies the computation.
#'
#' @param vector A numeric vector to be converted
#' @param origin The catalog symbol of the current unit.
#' @param target The catalog symbol of unit you want to convert to.
#'
#' @return
#' A numeric vector
#'
#' @examples
#' convert(1:20, "kg", "g")
#' convert(1:20, "galUK/min.ft2", "kft/s")
#' \dontrun{
#' convert(1:20, "kg", "km2")
#' }
#'
#' @export
#'
convert <- function(vector, origin, target) {
  if(!is.numeric(vector)){
    warning("Non-numeric input coerced to numeric.")
    vector <- as.numeric(vector)
  }

  if(!is_supported_unit(origin)){
    stop(paste(origin, "is not a supported unit."))
  }

  if (!is_supported_unit(target)) {
    stop(paste(target, "is not a supported unit."))
  }

  record_1 <- conversion_table[conversion_table$catalog_symbol == origin,]
  record_2 <- conversion_table[conversion_table$catalog_symbol == target,]

  if (record_1$base_unit != record_2$base_unit) {
    stop("Incompatible unit types")
  }

  base_units <- (record_1$a + record_1$b * vector) /
    (record_1$c + record_1$d * vector)
  out <- (base_units * record_2$c - record_2$a) / (record_2$b - record_2$d)

  return(out)
}

#' Check whether a unit can be converted.
#'
#' @noRd
#' @param unit
#' Name of Unit to be converted
is_supported_unit <- function(unit) {
  return(unit %in% conversion_table$catalog_symbol)
}

#' @title Return the conversion table
#' @description A convenience function to return \code{\link{conversion_table}}
#'
#' @return
#' Conversion table dataframe
#' @export
#'
#' @examples
#' a <-  get_conversion_table()
get_conversion_table <- function(){
  conversion_table
}

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convertr documentation built on May 29, 2017, 5:14 p.m.