support vctrs abbreviations

[sebkopf]

Suggested fix for #1487 , this follows the equivalent use of vctrs::vec_ptype_abbr in the pillar package (see code).

Note that it would be possible to replace the paged_table_type_sum() function almost entirely with what is implemented broadly by the vctrs::vec_ptype_abbr generic (see e.g. implementation for atomic data types, date time, and factors) but it would introduce small differences (e.g. the factor abbreviation would become fct instead of fctr) and I wasn't sure if this is something you'd be interested in.

ps: since this is my first pull request to rstudio, I have sent the signed contributor agreement to jj@rstudio.com

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[yihui]

Thanks!

[yihui]

I'm hesitant on introducing a new dependency only for the purpose of supporting a specific feature html_document(df_print = "paged"). I'm okay if it is in Suggests, and we call it conditionally, e.g., if (xfun::loadable('vctrs')) return(vctrs:: vec_ptype_abbr(x)).

If the difference between the output of rmarkdown:::paged_table_type_sum() and vctrs::vec_ptype_abbr() is minor, I tend to fix the difference to make them consistent.

[sebkopf]

Thank you, I moved vctrs to suggests and included the check whether the package is installed. This should work well since anyone who wants to make use of vctrs in a paged table will have it installed anyways. Could also skip the suggests altogether since tibble is already on the suggests list for rmarkdown and tibble depends on vctrs.

With this, these kind of vctrs-type vector implementations now print similarly in standard output and paged tables:

library(vctrs)
percent <- function(x = double()) {
  vec_assert(x, double())
  new_vctr(x, class = "percent")
}
format.percent <- function(x, ...) {
  paste0(formatC(signif(vec_data(x) * 100, 3)), "%")
}
vec_ptype_abbr.percent <- function(x, ...) "prcnt"

df <- tibble::tibble(x = percent(runif(4)))

in a knitted R markdown file, df prints as:

## # A tibble: 4 x 1
##         x
##   <prcnt>
## 1   14.1%
## 2   51.5%
## 3   65.5%
## 4   95.5%

and rmarkdown::paged_table(df) now also as

[yihui]

Great. Thanks!

[cderv]

Is this a confidential feature or should we add a bullet to NEWS ? 😄

[yihui]

Not confidential but I thought it was a rather minor change and probably not worth mentioning :) Please feel free to add a bullet.