Feature request: Option to print both head and tail of tables? about pillar

[DarwinAwardWinner]

I had a look through the code to see if I could implement this myself, but there were a few too many layers of indirection for me to follow. If you can point me to the appropriate place in the code, I can try implementing this when I have time.

[krlmlr]

Thanks. The prt package implements output in this way, see, e.g., https://github.com/nbenn/prt/blob/main/tests/testthat/_snaps/format.md .

CC @nbenn.

[DarwinAwardWinner]

Interesting. So it looks like I could potentially define my own print method for data frames and/or tibbles that calls prt::format_dt. Is there an easy way to determine if a given tibble's backend supports efficient random access so that I can avoid trying to e.g. get the tail of a database query result?

[krlmlr]

None that I'm aware of, perhaps you could implement some heuristics? Happy to review if you'd be willing to share an implementation.

[DarwinAwardWinner]

I will definitely share if I figure it out. Do you have any opinions on how the options should be set up?

[DarwinAwardWinner]

A minimal implementation for tibbles, meant to be put in ~/.Rprofile:

print.tbl <- function (x, width = NULL, ..., n = NULL, max_extra_cols = NULL, max_footer_lines = NULL) {
    tryCatch({
        n_half <- if(!is.null(n)) ceiling(n/2)
        prt:::cat_line(prt:::format_dt(x = x, ..., n = n_half, width = width, max_extra_cols = max_extra_cols, max_footer_lines = max_footer_lines))
    }, error = \(...) pillar:::print.tbl(x = x, width = width, ..., n = n, max_extra_cols = max_extra_cols, max_footer_lines = max_footer_lines))
}

I also came up with something for base data frames, but I print them using the aforementioned S4Vectors code, since the dplyr/pillar stuff doesn't print row names, which can't be ignored for base data frames.

print.data.frame <- function(x, ...) {
    tryCatch({
        withr::with_options(
            list(max.print = ncol(x) * 15),
            S4Vectors:::.show_DataFrame(x)
        )
    }, error = \(...) base::print.data.frame(x = x, ...))
}