Decimal alignment with cols_align_decimal()

[rich-iannone]

This adds the cols_align_decimal() function, which is to be used for lining up numeric values by the decimal mark. The function ensures that columns targeted are right-aligned, that accounting notation is supported, and that footnote marks don't interfere.

Fixes: #139
Fixes: #144
Fixes: #560
Fixes: #673

[cscheid]

I know some people who literally refuse to use anything but LaTeX tables exactly because of this feature!

[cscheid]

@domoritz Sorry to randomly tag you on this, but check out what's coming to quarto's tables soon! 😍 https://github.com/rstudio/gt/pull/1058/files#diff-0561d116b26297ef34a596107e310c46f00d108472133cc5468dc644fe0e124f

[cscheid]

This looks excellent.

[domoritz]

😍 that's awesome. Thank you for randomly tagging me.

[steveputman]

This is great, @rich-iannone!

It's fairly common, when using accounting = TRUE, that numbers are rounded (so decimals = 0). That combination of options (unless drop_trailing_dec_mark = FALSE is also used) doesn't align properly, which obviously makes sense given that there are no decimals for cols_align_decimal() to attack.

Do you think there's any way to address that combination of options (for example by (a) faking the decimal by imputing the drop_trailing_dec_mark = FALSE option, running align_to_char(), then stripping out the decimal or (b) applying the original approach of inserting an invisible parenthesis after nonnegative numbers)? Happy to take a stab but not sure of the best approach.

Thanks!

library(gt)

dplyr::tibble(
  char = LETTERS[1:8],
  num = c(1.2, -33.52, 9023.2, -283.527, 0.401, -123.1, NA, 41)) |> 
  gt() |> 
  tab_header("fmt_currency / accounting = TRUE / decimals = 0") |> 
  fmt_currency(num, accounting = TRUE, decimals = 0) |> 
  cols_align_decimal()

fmt_currency / accounting = TRUE / decimals = 0
char	num
A	$1
B	($34 )
C	$9,023
D	($284 )
E	$0
F	($123 )
G	NA
H	$41

^{Created on 2022-10-13 with reprex v2.0.2}