fmt_fraction: Format values as mixed fractions

View source: R/format_data.R

fmt_fractionR Documentation

Format values as mixed fractions


With numeric values in a gt table, we can perform mixed-fraction-based formatting. There are several options for setting the accuracy of the fractions. Furthermore, there is an option for choosing a layout (i.e., typesetting style) for the mixed-fraction output.

The following options are available for controlling this type of formatting:

  • accuracy: how to express the fractional part of the mixed fractions; there are three keyword options for this and an allowance for arbitrary denominator settings

  • simplification: an option to simplify fractions whenever possible

  • layout: We can choose to output values with diagonal or inline fractions

  • digit grouping separators: options to enable/disable digit separators and provide a choice of separator symbol for the whole number portion

  • pattern: option to use a text pattern for decoration of the formatted mixed fractions

  • locale-based formatting: providing a locale ID will result in number formatting specific to the chosen locale


  columns = everything(),
  rows = everything(),
  accuracy = NULL,
  simplify = TRUE,
  layout = c("inline", "diagonal"),
  use_seps = TRUE,
  pattern = "{x}",
  sep_mark = ",",
  system = c("intl", "ind"),
  locale = NULL



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 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. Examples of select helper functions include starts_with(), ends_with(), contains(), matches(), one_of(), num_range(), and everything().


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. Examples of select helper functions include starts_with(), ends_with(), contains(), matches(), one_of(), 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).


Accuracy of fractions

⁠singl-kw:[low|med|high]|scalar<numeric|integer>(val>=1)⁠ // default: "low"

The type of fractions to generate. This can either be one of the keywords "low", "med", or "high" (to generate fractions with denominators of up to 1, 2, or 3 digits, respectively) or an integer value greater than zero to obtain fractions with a fixed denominator (2 yields halves, 3 is for thirds, 4 is quarters, etc.). For the latter option, using simplify = TRUE will simplify fractions where possible (e.g., 2/4 will be simplified as 1/2). By default, the "low" option is used.


Simplify the fraction

⁠scalar<logical>⁠ // default: TRUE

If choosing to provide a numeric value for accuracy, the option to simplify the fraction (where possible) can be taken with TRUE (the default). With FALSE, denominators in fractions will be fixed to the value provided in accuracy.


Layout of fractions in HTML output

⁠singl-kw:[inline|diagonal]⁠ // default: "inline"

For HTML output, the "inline" layout is the default. This layout places the numerals of the fraction on the baseline and uses a standard slash character. The "diagonal" layout will generate fractions that are typeset with raised/lowered numerals and a virgule.


Use digit group separators

⁠scalar<logical>⁠ // default: TRUE

An option to use digit group separators. The type of digit group separator is set by sep_mark and overridden if a locale ID is provided to locale. This setting is TRUE by default.


Specification of the formatting pattern

⁠scalar<character>⁠ // default: "{x}"

A formatting pattern that allows for decoration of the formatted value. The formatted value is represented by the {x} (which can be used multiple times, if needed) and all other characters will be interpreted as string literals.


Separator mark for digit grouping

⁠scalar<character>⁠ // default: ","

The string to use as a separator between groups of digits. For example, using sep_mark = "," with a value of 1000 would result in a formatted value of "1,000". This argument is ignored if a locale is supplied (i.e., is not NULL).


Numbering system for grouping separators

⁠singl-kw:[intl|ind]⁠ // default: "intl"

The international numbering system (keyword: "intl") is widely used and its grouping separators (i.e., sep_mark) are always separated by three digits. The alternative system, the Indian numbering system (keyword: "ind"), uses grouping separators that correspond to thousand, lakh, crore, and higher quantities.


Locale identifier

⁠scalar<character>⁠ // default: NULL (optional)

An optional locale identifier that can be used for formatting values according the locale's rules. Examples include "en" for English (United States) and "fr" for French (France). We can use the info_locales() function as a useful reference for all of the locales that are supported. A locale ID can be also set in the initial gt() function call (where it would be used automatically by any function with a locale argument) but a locale value provided here will override that global locale.


An object of class gt_tbl.

Compatibility of formatting function with data values

The fmt_fraction() formatting function is compatible with body cells that are of the "numeric" or "integer" types. Any other types of body cells are ignored during formatting. This is to say that cells of incompatible data types may be targeted, but there will be no attempt to format them.

Targeting cells with columns and rows

Targeting of values is done through columns and additionally by rows (if nothing is provided for rows then entire columns are selected). The columns argument allows us to target a subset of cells contained in the resolved columns. We say resolved because aside from declaring column names in c() (with bare column names or names in quotes) we can use tidyselect-style expressions. This can be as basic as supplying a select helper like starts_with(), or, providing a more complex incantation like

where(~ is.numeric(.x) && max(.x, na.rm = TRUE) > 1E6)

which targets numeric columns that have a maximum value greater than 1,000,000 (excluding any NAs from consideration).

By default all columns and rows are selected (with the everything() defaults). Cell values that are incompatible with a given formatting function will be skipped over, like character values and numeric ⁠fmt_*()⁠ functions. So it's safe to select all columns with a particular formatting function (only those values that can be formatted will be formatted), but, you may not want that. One strategy is to format the bulk of cell values with one formatting function and then constrain the columns for later passes with other types of formatting (the last formatting done to a cell is what you get in the final output).

Once the columns are targeted, we may also target the rows within those columns. This can be done in a variety of ways. If a stub is present, then we potentially have row identifiers. Those can be used much like column names in the columns-targeting scenario. We can use simpler tidyselect-style expressions (the select helpers should work well here) and we can use quoted row identifiers in c(). It's also possible to use row indices (e.g., c(3, 5, 6)) though these index values must correspond to the row numbers of the input data (the indices won't necessarily match those of rearranged rows if row groups are present). One more type of expression is possible, an expression that takes column values (can involve any of the available columns in the table) and returns a logical vector. This is nice if you want to base formatting on values in the column or another column, or, you'd like to use a more complex predicate expression.

Compatibility of arguments with the from_column() helper function

The from_column() helper function can be used with certain arguments of fmt_fraction() to obtain varying parameter values from a specified column within the table. This means that each row could be formatted a little bit differently. These arguments provide support for from_column():

  • accuracy

  • simplify

  • layout

  • use_seps

  • pattern

  • sep_mark

  • system

  • locale

Please note that for all of the aforementioned arguments, a from_column() call needs to reference a column that has data of the correct type (this is different for each argument). Additional columns for parameter values can be generated with the cols_add() function (if not already present). Columns that contain parameter data can also be hidden from final display with cols_hide(). Finally, there is no limitation to how many arguments the from_column() helper is applied so long as the arguments belong to this closed set.

Adapting output to a specific locale

This formatting function can adapt outputs according to a provided locale value. Examples include "en" for English (United States) and "fr" for French (France). The use of a valid locale ID here means separator and decimal marks will be correct for the given locale. Should any value be provided in sep_mark, it will be overridden by the locale's preferred values.

Note that a locale value provided here will override any global locale setting performed in gt()'s own locale argument (it is settable there as a value received by all other functions that have a locale argument). As a useful reference on which locales are supported, we can use the info_locales() function to view an info table.


Using a summarized version of the pizzaplace dataset, let's create a gt table. With the fmt_fraction() function we can format the f_sold and f_income columns to display fractions. As for how the fractions are represented, we are electing to use accuracy = 10. This gives all fractions as tenths. We won't simplify the fractions (by using simplify = FALSE) and this means that a fraction like 5/10 won't become 1/2. With layout = "diagonal", we get a diagonal display of all fractions.

pizzaplace |>
  dplyr::group_by(type, size) |>
    sold = dplyr::n(),
    income = sum(price),
    .groups = "drop_last"
  ) |>
  dplyr::group_by(type) |>
    f_sold = sold / sum(sold),
    f_income = income / sum(income),
  ) |>
  dplyr::arrange(type, dplyr::desc(income)) |>
  gt(rowname_col = "size") |>
    title = "Pizzas Sold in 2015",
    subtitle = "Fraction of Sell Count and Revenue by Size per Type"
  ) |>
  fmt_integer(columns = sold) |>
  fmt_currency(columns = income) |>
    columns = starts_with("f_"),
    accuracy = 10,
    simplify = FALSE,
    layout = "diagonal"
  ) |>
  sub_missing(missing_text = "") |>
    label = "Sold",
    columns = contains("sold")
  ) |>
    label = "Revenue",
    columns = contains("income")
  ) |>
    locations = cells_body(),
    fn = function(x) {
        x == 0 ~ "<em>nil</em>",
        x != 0 ~ x
  ) |>
    sold = "Amount",
    income = "Amount",
    f_sold = md("_f_"),
    f_income = md("_f_")
  ) |>
  cols_align(align = "center", columns = starts_with("f")) |>
    table.width = px(400),
    row_group.as_column = TRUE
This image of a table was generated from the first code example in the `fmt_fraction()` help file.

Function ID


Function Introduced

v0.4.0 (February 15, 2022)

See Also

The vector-formatting version of this function: vec_fmt_fraction().

Other data formatting functions: data_color(), fmt_auto(), fmt_bins(), fmt_bytes(), fmt_currency(), fmt_datetime(), fmt_date(), fmt_duration(), fmt_engineering(), fmt_flag(), fmt_icon(), fmt_image(), fmt_index(), fmt_integer(), fmt_markdown(), fmt_number(), fmt_partsper(), fmt_passthrough(), fmt_percent(), fmt_roman(), fmt_scientific(), fmt_spelled_num(), fmt_time(), fmt_units(), fmt_url(), fmt(), sub_large_vals(), sub_missing(), sub_small_vals(), sub_values(), sub_zero()

gt documentation built on Oct. 7, 2023, 9:07 a.m.