Some slight speedups of convert units

R/general.R

@@ -246,32 +246,13 @@ plot_ions <- function(water) {
     guides(fill = "none")
 }
 
-
-#' @title Calculate unit conversions for common compounds
-#'
-#' @description This function takes a value and converts units based on compound name.
-#'
-#' @param value Value to be converted
-#' @param formula Chemical formula of compound. Accepts compounds in mweights for conversions between g and mol or eq
-#' @param startunit Units of current value, currently accepts g/L; g/L CaCO3; g/L N; M; eq/L;
-#' and the same units with "m", "u", "n" prefixes
-#' @param endunit Desired units, currently accepts same as start units
-#'
-#' @examples
-#' convert_units(50, "ca") # converts from mg/L to M by default
-#' convert_units(50, "ca", "mg/L", "mg/L CaCO3")
-#' convert_units(50, "ca", startunit = "mg/L", endunit = "eq/L")
-#'
-#' @export
-#'
-#' @returns A numeric value for the converted parameter.
-#'
-convert_units <- function(value, formula, startunit = "mg/L", endunit = "M") {
-  milli_list <- c("mg/L", "mg/L CaCO3", "mg/L N", "mM", "meq/L")
-  mcro_list <- c("ug/L", "ug/L CaCO3", "ug/L N", "uM", "ueq/L")
-  nano_list <- c("ng/L", "ng/L CaCO3", "ng/L N", "nM", "neq/L")
-  stand_list <- c("g/L", "g/L CaCO3", "g/L N", "M", "eq/L")
-
+# Internal conversion function
+# This function generates a cached table of unit conversions with every combo of formula and units in the compile_tidywater_data file.
+# If we fail to lookup a unit conversion in our cached table we look here
+# This function is ~20x slower than the cache lookup
+convert_units_private <- function(value, formula, startunit = "mg/L", endunit = "M") {
+  unit_multipliers <- get("unit_multipliers")
+  formula_to_charge <- get("formula_to_charge")
   gram_list <- c(
     "ng/L", "ug/L", "mg/L", "g/L",
     "ng/L CaCO3", "ug/L CaCO3", "mg/L CaCO3", "g/L CaCO3",
@@ -283,37 +264,15 @@ convert_units <- function(value, formula, startunit = "mg/L", endunit = "M") {
   caco_list <- c("mg/L CaCO3", "g/L CaCO3", "ug/L CaCO3", "ng/L CaCO3")
   n_list <- c("mg/L N", "g/L N", "ug/L N", "ng/L N")
 
-  # Determine multiplier for order of magnitude conversion
-  # In the same list, no multiplier needed
-  if ((startunit %in% milli_list & endunit %in% milli_list) |
-    (startunit %in% stand_list & endunit %in% stand_list) |
-    (startunit %in% nano_list & endunit %in% nano_list) |
-    (startunit %in% mcro_list & endunit %in% mcro_list)) {
-    multiplier <- 1
-    # m - standard, n-u, u-n
-  } else if ((startunit %in% milli_list & endunit %in% stand_list) |
-    (startunit %in% mcro_list & endunit %in% milli_list) |
-    (startunit %in% nano_list & endunit %in% mcro_list)) {
-    multiplier <- 1e-3
-  } else if ((startunit %in% stand_list & endunit %in% milli_list) |
-    (startunit %in% milli_list & endunit %in% mcro_list) |
-    (startunit %in% mcro_list & endunit %in% nano_list)) {
-    multiplier <- 1e3
-    # u - standard
-  } else if ((startunit %in% mcro_list & endunit %in% stand_list) |
-    (startunit %in% nano_list & endunit %in% milli_list)) {
-    multiplier <- 1e-6
-  } else if ((startunit %in% stand_list & endunit %in% mcro_list) |
-    (startunit %in% milli_list & endunit %in% nano_list)) {
-    multiplier <- 1e6
-    # n - standard
-  } else if (startunit %in% nano_list & endunit %in% stand_list) {
-    multiplier <- 1e-9
-  } else if (startunit %in% stand_list & endunit %in% nano_list) {
-    multiplier <- 1e9
-  } else {
+  # Look up the unit multipliers for starting and end units
+  start_mult <- unit_multipliers[[startunit]]
+  end_mult <- unit_multipliers[[endunit]]
+  if (is.null(start_mult) || is.null(end_mult)) {
+    # If we didn't find multipliers these units are not supported
     stop("Units not supported")
   }
+  # Calculate the net multiplier
+  multiplier <- start_mult / end_mult
 
   # Need molar mass of CaCO3 and N
   caco3_mw <- as.numeric(tidywater::mweights["caco3"])
@@ -333,16 +292,15 @@ convert_units <- function(value, formula, startunit = "mg/L", endunit = "M") {
   } else if (!(startunit %in% gram_list) & !(endunit %in% gram_list)) {
     molar_weight <- 0
   } else {
-    stop("Chemical formula not supported")
+    stop(paste("Chemical formula not supported: ", formula))
   }
 
   # Determine charge for equivalents
-  if (formula %in% c("na", "k", "cl", "hcl", "naoh", "nahco3", "na", "nh4", "f", "br", "bro3")) {
-    charge <- 1
-  } else if (formula %in% c("so4", "caco3", "h2so4", "na2co3", "caoh2", "mgoh2", "mg", "ca", "pb", "cacl2", "mn")) {
-    charge <- 2
-  } else if (formula %in% c("h3po4", "al", "fe", "alum", "fecl3", "fe2so43", "po4")) {
-    charge <- 3
+  # Look up our known charges in our hashtable
+  table_charge <- formula_to_charge[[formula]]
+  if (!is.null(table_charge)) {
+    # If we found a charge in the hash table use that
+    charge <- table_charge
   } else if (!(startunit %in% eqvl_list) & !(endunit %in% eqvl_list)) {
     # This is included so that charge can be in equations later without impacting results
     charge <- 1
@@ -386,6 +344,37 @@ convert_units <- function(value, formula, startunit = "mg/L", endunit = "M") {
   }
 }
 
+#' @title Calculate unit conversions for common compounds
+#'
+#' @description This function takes a value and converts units based on compound name.
+#'
+#' @param value Value to be converted
+#' @param formula Chemical formula of compound. Accepts compounds in mweights for conversions between g and mol or eq
+#' @param startunit Units of current value, currently accepts g/L; g/L CaCO3; g/L N; M; eq/L;
+#' and the same units with "m", "u", "n" prefixes
+#' @param endunit Desired units, currently accepts same as start units
+#'
+#' @examples
+#' convert_units(50, "ca") # converts from mg/L to M by default
+#' convert_units(50, "ca", "mg/L", "mg/L CaCO3")
+#' convert_units(50, "ca", startunit = "mg/L", endunit = "eq/L")
+#'
+#' @export
+#'
+#' @returns A numeric value for the converted parameter.
+#'
+convert_units <- function(value, formula, startunit = "mg/L", endunit = "M") {
+  convert_units_cache <- get("convert_units_cache")
+  # Start with pre-generated lookup table (which has most combinations of formula and units) for speed.
+  lookup <- convert_units_cache[[paste(formula, startunit, endunit)]]
+  if (is.null(lookup)) {
+    # Fallback to full implementation
+    convert_units_private(value, formula, startunit, endunit)
+  } else {
+    value * lookup
+  }
+}
+
 
 #' @title Calculate hardness from calcium and magnesium
 #'

data-raw/compile_tidywater_data.R

@@ -785,3 +785,98 @@ bromatecoeffs <- data.frame(
     I = 1 # temp not in exponent
   )
 usethis::use_data(bromatecoeffs, overwrite = TRUE)
+
+# For all units accepted by the convert_units function
+# provide their SI base multipliers
+unit_multipliers <- data.frame(
+  # base
+  "g/L" = 1,
+  "g/L CaCO3" = 1,
+  "g/L N" = 1,
+  "M" = 1,
+  "eq/L" = 1,
+  # milli
+  "mg/L" = 1e-3,
+  "mg/L CaCO3" = 1e-3,
+  "mg/L N" = 1e-3,
+  "mM" = 1e-3,
+  "meq/L" = 1e-3,
+  # micro
+  "ug/L" = 1e-6,
+  "ug/L CaCO3" = 1e-6,
+  "ug/L N" = 1e-6,
+  "uM" = 1e-6,
+  "ueq/L" = 1e-6,
+  # nano
+  "ng/L" = 1e-9,
+  "ng/L CaCO3" = 1e-9,
+  "ng/L N" = 1e-9,
+  "nM" = 1e-9,
+  "neq/L" = 1e-9,
+  # required to allow names with slashes
+  check.names = FALSE
+)
+
+# Used as part of convert units
+# Provides a quick lookup of the charge of a given formula
+formula_to_charge <- data.frame(
+  "na" = 1,
+  "k" = 1,
+  "cl" = 1,
+  "hcl" = 1,
+  "naoh" = 1,
+  "nahco3" = 1,
+  "nh4" = 1,
+  "f" = 1,
+  "br" = 1,
+  "bro3" = 1,
+  "so4" = 2,
+  "caco3" = 2,
+  "h2so4" = 2,
+  "na2co3" = 2,
+  "caoh2" = 2,
+  "mgoh2" = 2,
+  "mg" = 2,
+  "ca" = 2,
+  "pb" = 2,
+  "cacl2" = 2,
+  "mn" = 2,
+  "h3po4" = 3,
+  "al" = 3,
+  "fe" = 3,
+  "alum" = 3,
+  "fecl3" = 3,
+  # TODO ASK SIERRA (fe2so43 is not in mweights)
+  # "fe2so43"= 3,
+  "po4" = 3
+)
+
+# This function is used to generate a fast lookup table to speed up unit conversions.
+# We precompute all permutations of our normal conversions and store them in a hash map.
+generate_unit_conversions_cache <- function() {
+  # All units we support
+  units <- ls(unit_multipliers)
+  # All formulas we support are in mweights, note this is more than formula_to_charge
+  formulas <- ls(mweights)
+  env <- new.env(parent = emptyenv())
+  for (startunit in units) {
+    for (endunit in units) {
+      for (formula in formulas) {
+        name <- paste(formula, startunit, endunit)
+        # Not all unit conversions will be valid
+        # Try them all and we won't store any that fail
+        try(
+          {
+            env[[name]] <- convert_units_private(1.0, formula, startunit, endunit)
+          },
+          silent = TRUE
+        )
+      }
+    }
+  }
+  env
+}
+
+convert_units_cache <- generate_unit_conversions_cache()
+
+usethis::use_data(unit_multipliers, formula_to_charge, convert_units_cache, overwrite = TRUE, internal = TRUE)