Unit conversion helper

NAMESPACE

@@ -160,6 +160,7 @@ export(info_icons)
 export(info_locales)
 export(info_paletteer)
 export(info_time_style)
+export(info_unit_conversions)
 export(local_image)
 export(matches)
 export(md)
@@ -218,6 +219,7 @@ export(text_case_match)
 export(text_case_when)
 export(text_replace)
 export(text_transform)
+export(unit_conversion)
 export(vars)
 export(vec_fmt_bytes)
 export(vec_fmt_currency)

R/helpers.R

@@ -524,6 +524,125 @@ currency <- function(
   currency_list
 }
 
+#' Get a conversion factor across two measurement units of a given class
+#'
+#' @description
+#'
+#' The `unit_conversion()` helper function gives us a conversion factor for
+#' transforming a value from one form of measurement units to a target form.
+#' For example if you have a length value that is expressed in miles you could
+#' transform that value to one in kilometers through multiplication of the value
+#' by the conversion factor (in this case `1.60934`).
+#'
+#' For `unit_conversion()` to understand the source and destination units, you
+#' need to provide a keyword value for the `from` and `to` arguments. To aid as
+#' a reference for this, call [info_unit_conversions()] to display an
+#' information table that contains all of the keywords for every conversion
+#' type.
+#'
+#' @param from *Units for the input value*
+#'
+#'   `scalar<character>` // **required**
+#'
+#'   The keyword representing the units for the value that requires unit
+#'   conversion. In the case where the value has units of miles, the necessary
+#'   input is `"length.mile"`.
+#'
+#' @param to *Desired units for the value*
+#'
+#'   `scalar<character>` // **required**
+#'
+#'   The keyword representing the target units for the value with units defined
+#'   in `from`. In the case where input value has units of miles and we would
+#'   rather want the value to be expressed as kilometers, the `to` value should
+#'   be `"length.kilometer"`.
+#'
+#' @return A single numerical value.
+#'
+#' @section Examples:
+#'
+#' Let's use a portion of the [`towny`] dataset and create a table showing
+#' population, density, and land area for 10 municipalities. The `land_area_km2`
+#' values are in units of square kilometers, however, we'd rather the values
+#' were in square miles. We can convert the numeric values while formatting the
+#' values with [`fmt_number()`] by using `unit_conversion()` in the `scale_by`
+#' argument since the return value of that is a conversion factor (which is
+#' applied to each value by multiplication). The same is done for converting the
+#' 'people per square kilometer' values in `density_2021` to 'people per square
+#' mile', however, the units to convert are in the denominator so the inverse
+#' of the conversion factor must be used.
+#'
+#' ```r
+#' towny |>
+#'   dplyr::arrange(desc(density_2021)) |>
+#'   dplyr::slice_head(n = 10) |>
+#'   dplyr::select(name, population_2021, density_2021, land_area_km2) |>
+#'   gt(rowname_col = "name") |>
+#'   fmt_integer(columns = population_2021) |>
+#'   fmt_number(
+#'     columns = land_area_km2,
+#'     decimals = 1,
+#'     scale_by = unit_conversion(
+#'       from = "area.square_kilometer",
+#'       to = "area.square_mile"
+#'     )
+#'   ) |>
+#'   fmt_number(
+#'     columns = density_2021,
+#'     decimals = 1,
+#'     scale_by = 1 / unit_conversion(
+#'       from = "area.square_kilometer",
+#'       to = "area.square_mile"
+#'     )
+#'   ) |>
+#'   cols_label(
+#'     land_area_km2 = "Land Area,<br>sq. mi",
+#'     population_2021 = "Population",
+#'     density_2021 = "Density,<br>ppl / sq. mi",
+#'     .fn = md
+#'   )
+#' ```
+#'
+#' \if{html}{\out{
+#' `r man_get_image_tag(file = "man_unit_conversion_1.png")`
+#' }}
+#'
+#' @family helper functions
+#' @section Function ID:
+#' 8-7
+#'
+#' @section Function Introduced:
+#' *In Development*
+#'
+#' @export
+unit_conversion <- function(from, to) {
+
+  force(from)
+  force(to)
+
+  if (!(from %in% conversion_factors[["from"]])) {
+    cli::cli_abort("The unit supplied in {.arg from} is not known.")
+  }
+  if (!(to %in% conversion_factors[["to"]])) {
+    cli::cli_abort("The unit supplied in {.arg to} is not known.")
+  }
+
+  if (from == to) {
+    return(1.0)
+  }
+
+  row_conversion <-
+    dplyr::filter(conversion_factors, from == {{ from }}, to == {{ to }})
+
+  # In the case where units are valid and available in the internal dataset,
+  # they may be across categories; such pairings do not allow for a conversion
+  # to take place
+  if (nrow(row_conversion) < 1) {
+    cli::cli_abort("The conversion specified cannot be performed.")
+  }
+
+  row_conversion[["conv_factor"]]
+}
 
 #' Supply nanoplot options to `cols_nanoplot()`
 #'
@@ -778,7 +897,7 @@ currency <- function(
 #'
 #' @family helper functions
 #' @section Function ID:
-#' 8-7
+#' 8-8
 #'
 #' @section Function Introduced:
 #' `v0.10.0` (October 7, 2023)
@@ -984,7 +1103,7 @@ nanoplot_options <- function(
 #'
 #' @family helper functions
 #' @section Function ID:
-#' 8-8
+#' 8-9
 #'
 #' @section Function Introduced:
 #' `v0.2.0.5` (March 31, 2020)

R/info_tables.R

@@ -824,3 +824,41 @@ info_flags <- function() {
 info_icons <- function() {
   readRDS(system_file("gt_tables/info_icons.rds"))
 }
+
+#' View a table with all units that can be converted by `unit_conversion()`
+#'
+#' @description
+#'
+#' [unit_conversion()] can be used to yield conversion factors across compatible
+#' pairs of units. This is useful for expressing values in different units and
+#' the conversion can be performed via the `scale_by` argument available in
+#' several formatting functions. When calling [unit_conversion()], one must
+#' supply two string-based keywords to specify the value's current units and the
+#' desired units. All of these keywords are provided in the table shown by
+#' calling `info_unit_conversions()`.
+#'
+#' @return An object of class `gt_tbl`.
+#'
+#' @section Examples:
+#'
+#' Get a table of info on all the available keywords for unit conversions.
+#'
+#' ```r
+#' info_unit_conversions()
+#' ```
+#'
+#' \if{html}{\out{
+#' `r man_get_image_tag(file = "man_info_unit_conversions_1.png")`
+#' }}
+#'
+#' @family information functions
+#' @section Function ID:
+#' 11-9
+#'
+#' @section Function Introduced:
+#' *In Development*
+#'
+#' @export
+info_unit_conversions <- function() {
+  readRDS(system_file("gt_tables/info_conversions.rds"))
+}

data-raw/X01-currencies.R

@@ -5,3 +5,6 @@ currencies <-
     file = "data-raw/x_currencies.csv",
     col_types = "ccccc"
   )
+
+# Drop spec() attribute
+currencies <- currencies[]

data-raw/X02-currency_symbols.R

@@ -5,3 +5,6 @@ currency_symbols <-
     file = "data-raw/x_currency_symbols.csv",
     col_types = "cc"
   )
+
+# Drop spec() attribute
+currency_symbols <- currency_symbols[]

data-raw/X07-fractions.R

@@ -5,3 +5,6 @@ fractions <-
     file = "data-raw/fractions.csv",
     col_types = "ccccccccc"
   )
+
+# Drop spec() attribute
+fractions <- fractions[]

data-raw/X10-spelled_num.R

@@ -87,3 +87,6 @@ spelled_num <-
       zh = col_character()
     )
   )
+
+# Drop spec() attribute
+spelled_num <- spelled_num[]

data-raw/X12-country_names.R

@@ -6,3 +6,6 @@ country_names <-
     col_types = cols(.default = col_character()),
     na = ""
   )
+
+# Drop spec() attribute
+country_names <- country_names[]

data-raw/X13-country_names_additional.R

@@ -6,3 +6,6 @@ country_names_additional <-
     col_types = cols(.default = col_character()),
     na = ""
   )
+
+# Drop spec() attribute
+country_names_additional <- country_names_additional[]

data-raw/X14-tf_words.R

@@ -5,3 +5,6 @@ tf_words <-
     file = "data-raw/tf_words.csv",
     col_types = cols(.default = col_character())
   )
+
+# Drop spec() attribute
+tf_words <- tf_words[]

data-raw/X15-conversion_factors.R

@@ -0,0 +1,15 @@
+library(tidyverse)
+
+conversion_factors <-
+  readr::read_csv(
+    file = "data-raw/conversion_factors.csv",
+    col_types = cols(
+      type = col_character(),
+      from = col_character(),
+      to = col_character(),
+      conv_factor = col_double()
+    )
+  )
+
+# Drop spec() attribute
+conversion_factors <- conversion_factors[]