Customize border colors dynamically in gt table

Question

I have a gt table that requires borders in several columns. I'm easily able to change the color of a targeted row and/or column, as you can see in this example with changing the border of "fig" to purple.

library(dplyr)
library(gt)

exibble %>%
  gt() %>%
  cols_align(align = "center",
             columns = c("char")) %>%
  tab_style(
    style = list(
      cell_borders(
        sides = c("all"),
        color = c("purple"),
        weight = px(3)
      )
    ),
    locations = list(
      cells_body(
        columns = "char",
        rows = char == "fig"
      )
    )
  )

However, when I try to change multiple colors at once from another column containing colors, I get an error:

exibble %>%
  mutate(col = case_when(char == "fig" ~ "purple",
                         char == "banana" ~ "yellow",
                         TRUE ~ "white")) %>%
  gt() %>%
  cols_align(align = "center",
             columns = c("char")) %>%
  tab_style(
    style = list(
      cell_borders(
        sides = c("all"),
        color = from_column(col),
        weight = px(3)
      )
    ),
    locations = list(
      cells_body(
        columns = "char",
        rows = !is.na(col)
      )
    )
  )

Error in `cell_borders()`:
! `color` must have a length one, not 3.

How do I make the entire column reflect the intended border colors (white, purple, or yellow) without having to one by one target those cell values?

Answer 1

As cell_borders does not accept vectorized color input your best bet is a loop. purrr::reduce is quite handy for such cases:

dat <- exibble %>%
  mutate(col = case_when(char == "fig" ~ "purple",
                         char == "banana" ~ "yellow",
                         TRUE ~ "white"))
tt <- dat %>%
  gt() %>%
  cols_align(align = "center",
             columns = c("char"))

## define color table with the row indices for targetting the right row
col_dat <- dat %>%
  mutate(rn = 1:n(), col, char, .keep = "none") %>%
  filter(!is.na(char))

## use reduce to apply a border color to each row separately

purrr::reduce(1:nrow(col_dat), function(tab, idx) {
  sl <- col_dat %>% slice(idx)
  tab %>%
    tab_style(
      style = list(
        cell_borders(
          sides = "all",
          color = sl %>% pull(col),
          weight = px(3)
        )
      ),
      locations = list(
        cells_body(
          columns = "char",
          rows = sl %>% pull(rn)
        )
      )
    )
}, .init = tt)