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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.


unit_conversion(from, to)



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".


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".


A single numerical value.


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.

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) |>
    columns = land_area_km2,
    decimals = 1,
    scale_by = unit_conversion(
      from = "area.square-kilometer",
      to = "area.square-mile"
  ) |>
    columns = density_2021,
    decimals = 1,
    scale_by = 1 / unit_conversion(
      from = "area.square-kilometer",
      to = "area.square-mile"
  ) |>
    land_area_km2 = "Land Area,<br>sq. mi",
    population_2021 = "Population",
    density_2021 = "Density,<br>ppl / sq. mi",
    .fn = md

This image of a table was generated from the first code example in the `unit_conversion()` help file.

With a small slice of the gibraltar dataset, let's display the temperature values in terms of degrees Celsius (present in the data) and as temperatures in degrees Fahrenheit (achievable via conversion). We can duplicate the temp column through cols_add() (naming the new column as temp_f) and when formatting through fmt_integer() we can call unit_conversion() within the scale_by argument to perform this transformation while formatting the values as integers.

gibraltar |>
    date == "2023-05-15",
    time >= "06:00",
    time <= "12:00"
  ) |>
  dplyr::select(time, temp) |>
  gt() |>
    title = "Air Temperature During Late Morning Hours at LXGB Stn.",
    subtitle = "May 15, 2023"
  ) |>
  cols_add(temp_f = temp) |>
  cols_move(columns = temp_f, after = temp) |>
    label = "Temperature",
    columns = starts_with("temp")
  ) |>
    columns = temp,
    decimals = 1
  ) |>
    columns = temp_f,
    scale_by = unit_conversion(
      from = "temperature.C",
      to = "temperature.F"
  ) |>
    time = "Time",
    temp = "{{degC}}",
    temp_f = "{{degF}}"
  ) |>
    starts_with("temp") ~ px(80),
    time ~ px(100)
  ) |>
  opt_horizontal_padding(scale = 3) |>
  opt_vertical_padding(scale = 0.5) |>
  opt_align_table_header(align = "left") |>
  tab_options(heading.title.font.size = px(16))

This image of a table was generated from the second code example in the `unit_conversion()` help file.

Function ID


Function Introduced

v0.11.0 (July 9, 2024)