Add the fmt_tf() function

[rich-iannone]

For those times where you have logical values in a gt table, you might want to express them in a slightly different way. You could express as a 'yes' or 'no', a 'true' or 'false', or, perhaps use pairings of complementary symbols that make sense in a table. The fmt_tf() function has a set of tf_style presets that can be used to quickly map TRUE/FALSE values to strings (which are automatically translated according to a given locale value), or, symbols like up/down or left/right arrows and open/closed shapes.

Here's an example of this, using the sp500 dataset:

library(tidyverse)
library(gt)

sp500 |>
  dplyr::filter(date >= "2013-01-07" & date <="2013-01-12") |>
  dplyr::arrange(date) |>
  dplyr::select(-c(adj_close, volume, high, low)) |>
  gt(rowname_col = "date") |>
  cols_add(dir = close > open, .after = open) |>
  fmt_tf(
    columns = dir,
    tf_style = "arrows",
    colors = c("green", "red")
  ) |>
  fmt_currency(columns = c(open, close)) |>
  cols_label(
    open = "Opening",
    close = "Closing",
    dir = ""
  )

Fixes: #1650