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The fmt() function provides a way to execute custom formatting functionality with raw data values in a way that can consider all output contexts.

Along with the columns and rows arguments that provide some precision in targeting data cells, the fns argument allows you to define one or more functions for manipulating the raw data.

If providing a single function to fns, the recommended format is in the form: fns = function(x) .... This single function will format the targeted data cells the same way regardless of the output format (e.g., HTML, LaTeX, RTF).

If you require formatting of x that depends on the output format, a list of functions can be provided for the html, latex, rtf, and default contexts. This can be in the form of fns = list(html = function(x) ..., latex = function(x) ..., default = function(x) ...). In this multiple-function case, we recommended including the default function as a fallback if all contexts aren't provided.


fmt(data, columns = everything(), rows = everything(), compat = NULL, fns)



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).


Formatting compatibility

vector<character> --- default: NULL (optional)

An optional vector that provides the compatible classes for the formatting. By default this is NULL.


Formatting functions

function|list of functions --- required

Either a single formatting function or a named list of functions.


An object of class gt_tbl.

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.


Use the exibble dataset to create a gt table. Using the fmt() function, we'll format the numeric values in the num column with a function supplied to the fns argument. This supplied function will take values in the column (x), multiply them by 1000, and exclose them in single quotes.

exibble |>
  dplyr::select(-row, -group) |>
  gt() |>
    columns = num,
    fns = function(x) {
      paste0("'", x * 1000, "'")

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

Function ID


Function Introduced

v0.2.0.5 (March 31, 2020)