Format measurement units

fmt_units() lets you better format measurement units in the table body. These must conform to gt's specialized units notation (e.g., "J Hz^-1 mol^-1" can be used to generate units for the molar Planck constant) for the best conversion. The notation here provides several conveniences for defining units, so as long as the values to be formatted conform to this syntax, you'll obtain nicely-formatted units no matter what the table output format might be (i.e., HTML, LaTeX, RTF, etc.). Details pertaining to the units notation can be found in the section entitled How to use gt's units notation.

Usage

fmt_units(data, columns = everything(), rows = everything())

Arguments

data

The gt table data object

obj:<gt_tbl> // required

This is the gt table object that is commonly created through use of the gt() function.

columns

Columns to target

<column-targeting expression> // default: everything()

Can either be a series of column names provided in c(), a vector of column indices, or a select helper function (e.g. starts_with(), ends_with(), contains(), matches(), num_range() and everything()).

rows

Rows to target

<row-targeting expression> // default: everything()

In conjunction with columns, we can specify which of their rows should undergo formatting. The default everything() results in all rows in columns being formatted. Alternatively, we can supply a vector of row captions within c(), a vector of row indices, or a select helper function (e.g. starts_with(), ends_with(), contains(), matches(), num_range(), and everything()). We can also use expressions to filter down to the rows we need (e.g., [colname_1] > 100 & [colname_2] < 50).

Value

An object of class gt_tbl.

How to use gt's units notation

The units notation involves a shorthand of writing units that feels familiar and is fine-tuned for the task at hand. Each unit is treated as a separate entity (parentheses and other symbols included) and the addition of subscript text and exponents is flexible and relatively easy to formulate. This is all best shown with examples:

"m/s" and "m / s" both render as "m/s"
"m s^-1" will appear with the "-1" exponent intact
"m /s" gives the same result, as "/<unit>" is equivalent to "<unit>^-1"
"E_h" will render an "E" with the "h" subscript
"t_i^2.5" provides a t with an "i" subscript and a "2.5" exponent
"m[_0^2]" will use overstriking to set both scripts vertically
"g/L %C6H12O6%" uses a chemical formula (enclosed in a pair of "%" characters) as a unit partial, and the formula will render correctly with subscripted numbers
Common units that are difficult to write using ASCII text may be implicitly converted to the correct characters (e.g., the "u" in "ug", "um", "uL", and "umol" will be converted to the Greek mu symbol; "degC" and "degF" will render a degree sign before the temperature unit)
We can transform shorthand symbol/unit names enclosed in ":" (e.g., ":angstrom:", ":ohm:", etc.) into proper symbols
Greek letters can added by enclosing the letter name in ":"; you can use lowercase letters (e.g., ":beta:", ":sigma:", etc.) and uppercase letters too (e.g., ":Alpha:", ":Zeta:", etc.)
The components of a unit (unit name, subscript, and exponent) can be fully or partially italicized/emboldened by surrounding text with "*" or "**"

Examples

Let's use the illness dataset and create a new gt table. The units column contains character values in gt's specialized units notation (e.g., "x10^9 / L") so the fmt_units() function was used to better format those units.

illness |>
  gt() |>
  fmt_units(columns = units) |>
  sub_missing(columns = -starts_with("norm")) |>
  sub_missing(columns = c(starts_with("norm"), units), missing_text = "") |>
  sub_large_vals(rows = test == "MYO", threshold = 1200) |>
  fmt_number(
    decimals = 2,
    drop_trailing_zeros = TRUE
  ) |>
  tab_header(title = "Laboratory Findings for the YF Patient") |>
  tab_spanner(label = "Day", columns = starts_with("day")) |>
  cols_label_with(fn = ~ gsub("day_", "", .)) |>
  cols_merge_range(col_begin = norm_l, col_end = norm_u) |>
  cols_label(
    starts_with("norm") ~ "Normal Range",
    test ~ "Test",
    units ~ "Units"
  ) |>
  cols_width(
    starts_with("day") ~ px(80),
    everything() ~ px(120)
  ) |>
  tab_style(
    style = cell_text(align = "center"),
    locations = cells_column_labels(columns = starts_with("day"))
  ) |>
  tab_style(
    style = cell_fill(color = "aliceblue"),
    locations = cells_body(columns = c(test, units))
  ) |>
  opt_vertical_padding(scale = 0.4) |>
  opt_align_table_header(align = "left") |>
  tab_options(heading.padding = px(10))

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

The constants dataset contains values for hundreds of fundamental physical constants. We'll take a subset of values that have some molar basis and generate a gt table from that. Like the illness dataset, this one has a units column so, again, the fmt_units() function will be used to format those units. Here, the preference for typesetting measurement units is to have positive and negative exponents (e.g., not "<unit_1> / <unit_2>" but rather "<unit_1> <unit_2>^-1").

constants |>
  dplyr::filter(grepl("molar", name)) |>
  gt() |>
  cols_hide(columns = c(uncert, starts_with("sf"))) |>
  fmt_units(columns = units) |>
  fmt_scientific(columns = value, decimals = 3) |>
  tab_header(title = "Physical Constants Having a Molar Basis") |>
  tab_options(column_labels.hidden = TRUE)

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

Function ID

3-19

Function Introduced

v0.10.0 (October 7, 2023)