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With numeric values in a vector, we can format the values so that they are rendered as per mille, ppm, ppb, etc., quantities. The following list of keywords (with associated naming and scaling factors) is available to use within vec_fmt_partsper():

  • "per-mille": Per mille, (1 part in 1,000)

  • "per-myriad": Per myriad, (1 part in 10,000)

  • "pcm": Per cent mille (1 part in 100,000)

  • "ppm": Parts per million, (1 part in 1,000,000)

  • "ppb": Parts per billion, (1 part in 1,000,000,000)

  • "ppt": Parts per trillion, (1 part in 1,000,000,000,000)

  • "ppq": Parts per quadrillion, (1 part in 1,000,000,000,000,000)

The function provides a lot of formatting control and we can use the following options:

  • custom symbol/units: we can override the automatic symbol or units display with our own choice as the situation warrants

  • decimals: choice of the number of decimal places, option to drop trailing zeros, and a choice of the decimal symbol

  • digit grouping separators: options to enable/disable digit separators and provide a choice of separator symbol

  • value scaling toggle: choose to disable automatic value scaling in the situation that values are already scaled coming in (and just require the appropriate symbol or unit display)

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

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


  to_units = c("per-mille", "per-myriad", "pcm", "ppm", "ppb", "ppt", "ppq"),
  symbol = "auto",
  decimals = 2,
  drop_trailing_zeros = FALSE,
  drop_trailing_dec_mark = TRUE,
  scale_values = TRUE,
  use_seps = TRUE,
  pattern = "{x}",
  sep_mark = ",",
  dec_mark = ".",
  force_sign = FALSE,
  incl_space = "auto",
  locale = NULL,
  output = c("auto", "plain", "html", "latex", "rtf", "word")



A numeric vector.


A keyword that signifies the desired output quantity. This can be any from the following set: "per-mille", "per-myriad", "pcm", "ppm", "ppb", "ppt", or "ppq".


The symbol/units to use for the quantity. By default, this is set to "auto" and gt will choose the appropriate symbol based on the to_units keyword and the output context. However, this can be changed by supplying a string (e.g, using symbol = "ppbV" when to_units = "ppb").


An option to specify the exact number of decimal places to use. The default number of decimal places is 2.


A logical value that allows for removal of trailing zeros (those redundant zeros after the decimal mark).


A logical value that determines whether decimal marks should always appear even if there are no decimal digits to display after formatting (e.g, 23 becomes 23.). The default for this is TRUE, which means that trailing decimal marks are not shown.


Should the values be scaled through multiplication according to the keyword set in to_units? By default this is TRUE since the expectation is that normally values are proportions. Setting to FALSE signifies that the values are already scaled and require only the appropriate symbol/units when formatted.


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.


A formatting pattern that allows for decoration of the formatted value. The value itself is represented by {x} and all other characters are taken to be string literals.


The mark to use as a separator between groups of digits (e.g., using sep_mark = "," with 1000 would result in a formatted value of 1,000).


The character to use as a decimal mark (e.g., using dec_mark = "," with 0.152 would result in a formatted value of 0,152).


Should the positive sign be shown for positive values (effectively showing a sign for all values except zero)? If so, use TRUE for this option. The default is FALSE, where only negative numbers will display a minus sign. This option is disregarded when using accounting notation with accounting = TRUE.


An option for whether to include a space between the value and the symbol/units. The default is "auto" which provides spacing dependent on the mark itself. This can be directly controlled by using either TRUE or FALSE.


An optional locale ID that can be used for formatting the value according the locale's rules. Examples include "en" for English (United States) and "fr" for French (France). The use of a valid locale ID will override any values provided in sep_mark and dec_mark. We can use the info_locales() function as a useful reference for all of the locales that are supported.


The output style of the resulting character vector. This can either be "auto" (the default), "plain", "html", "latex", "rtf", or "word". In knitr rendering (i.e., Quarto or R Markdown), the "auto" option will choose the correct output value


A character vector.


Let's create a numeric vector for the next few examples:

num_vals <- c(10^(-3:-5), NA)

Using vec_fmt_partsper() with the default options will create a character vector where the resultant per mille values have two decimal places and NA values will render as "NA". The rendering context will be autodetected unless specified in the output argument (here, it is of the "plain" output type).

#> [1] "1.00‰" "0.10‰" "0.01‰" "NA"

We can change the output units to a different measure. If ppm units are desired then to_units = "ppm" can be used.

vec_fmt_partsper(num_vals, to_units = "ppm")

#> [1] "1,000.00 ppm" "100.00 ppm" "10.00 ppm" "NA"

We can change the decimal mark to a comma, and we have to be sure to change the digit separator mark from the default comma to something else (a period works here):

  to_units = "ppm",
  sep_mark = ".",
  dec_mark = ","

#> [1] "1.000,00 ppm" "100,00 ppm" "10,00 ppm" "NA"

If we are formatting for a different locale, we could supply the locale ID and let gt handle these locale-specific formatting options:

vec_fmt_partsper(num_vals, to_units = "ppm", locale = "es")

#> [1] "1.000,00 ppm" "100,00 ppm" "10,00 ppm" "NA"

As a last example, one can wrap the values in a pattern with the pattern argument. Note here that NA values won't have the pattern applied.

vec_fmt_partsper(num_vals, to_units = "ppm", pattern = "{x}V")

#> [1] "1,000.00 ppmV" "100.00 ppmV" "10.00 ppmV" "NA"

Function ID