Consider adding x and y tick labels columns to `layer_data()`

[jooyoungseo]

layer_data() provides useful information for people with and without visual impairments to better understand current ggplot object in a table form.

However, this data does not contain x/y labels so it is challenging to associate each x/y values with their corresponding labels.

For example, in the following bar plot, the x labels ("2seater", "compact", "midsize", "minivan", "pickup", "subcompact", "suv") are not contained in layer_data() data frame.

                 Of course, it is possible to retrieve them by defining a custom function just like what {BrailleR} does like below; however, being able to see all the labels along with their corresponding values in one data frame would not only be more desirable, but also be more stable and consistent.

Reprex

library(ggplot2)

g <- ggplot(mpg, aes(class)) + geom_bar()

g

layer_data(g)
#>    y count prop x flipped_aes PANEL group ymin ymax xmin xmax colour   fill
#> 1  5     5    1 1       FALSE     1     1    0    5 0.55 1.45     NA grey35
#> 2 47    47    1 2       FALSE     1     2    0   47 1.55 2.45     NA grey35
#> 3 41    41    1 3       FALSE     1     3    0   41 2.55 3.45     NA grey35
#> 4 11    11    1 4       FALSE     1     4    0   11 3.55 4.45     NA grey35
#> 5 33    33    1 5       FALSE     1     5    0   33 4.55 5.45     NA grey35
#> 6 35    35    1 6       FALSE     1     6    0   35 5.55 6.45     NA grey35
#> 7 62    62    1 7       FALSE     1     7    0   62 6.55 7.45     NA grey35
#>   size linetype alpha
#> 1  0.5        1    NA
#> 2  0.5        1    NA
#> 3  0.5        1    NA
#> 4  0.5        1    NA
#> 5  0.5        1    NA
#> 6  0.5        1    NA
#> 7  0.5        1    NA

# Use custom function
.getGGXTicks <- function(x, xbuild, layer) {
  # The location of this item is changing in an upcoming ggplot version
  if ("panel_ranges" %in% names(xbuild$layout)) {
    return(xbuild$layout$panel_ranges[[layer]]$x.labels) # ggplot 2.2.1
  } else {
    xlabs <- xbuild$layout$panel_params[[1]]$x$get_labels()
    return(xlabs[!is.na(xlabs)])
  }
}

.getGGXTicks(g, ggplot_build(g), 1)
#> [1] "2seater"    "compact"    "midsize"    "minivan"    "pickup"    
#> [6] "subcompact" "suv"

^{Created on 2022-10-02 with reprex v2.0.2}

Session info

sessioninfo::session_info()
#> ─ Session info ───────────────────────────────────────────────────────────────
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#>  ui       RTerm
#>  language (EN)
#>  collate  English_United States.utf8
#>  ctype    English_United States.utf8
#>  tz       America/Chicago
#>  date     2022-10-02
#>  pandoc   2.19.2 @ C:/PROGRA~3/CHOCOL~1/bin/ (via rmarkdown)
#> 
#> ─ Packages ───────────────────────────────────────────────────────────────────
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[thomasp85]

Hi JooYoung

layer_data() has always ever been intended for testing purposes and I'm a bit apprehensive about tacking on more information than the actual layer data for fear that it turns into some sort of catch-all function.

However, I do think we should think about providing a suite of functions that can extract relevant information about the final state of a plot for use with textual descriptions etc. We will soon have some more ressources for this so hopefully we can begin to build this out in the release following the one I'm currently preparing.

best
Thomas

[teunbrand]

I think it might be useful to build something like layer_data(), but for guide breaks, positions and labels. I've noticed people trying to access these values (i.e. #5029, #5063), and I think accessor functions, as mentioned here, are a great idea that leaves maintainers free to change internal structures as long as the accessors continue to work. The current internal structure for guides are poised to change again.