Horizontal y axis title above plot, left-justified

[BajczA475]

A lot of design guides argue that text should, as often as possible, be printed horizontally to align with how most humans naturally read. However, the default y-axis title in ggplot2 (and pretty much every software ever!) is vertical. This makes sense, but I do actually much prefer the aesthetic of the y-axis title being horizontal and left-justified above the plot, as summarized in my SO post here: https://stackoverflow.com/questions/79654995/in-ggplot2-in-r-how-should-i-position-a-y-axis-title-in-the-top-plot-margin-le

As I noted there, there are several "hack-y" ways to do this, but none that "just work" programmatically out of the box.

What I'd love to see is something akin to the legend.position theme element but for the y axis title. If I could just do y.axis.title.position = "top", where hjust could then be used to slide it to one edge or the other, that'd be awesome! I don't presume to know any of the technical difficulties of implementing that though....

[teunbrand]

Thanks for the suggestion! This would be the perview of Facet$draw_labels(), so that'd be a starting place to try to extend this functionality. How do you imagine this works with scale_x_discrete/continuous(position = "top") or guides(x.sec = "axis")? Would this be underneath facet strips or above?

[BajczA475]

Hmm these are really interesting questions! Just dabbling with those just now, my hot takes would be:

1. When position = "top" for the scale_x_* function, I imagine a plot whose vertical direction of interest is perhaps inverted (like, y is a measure of lake depth or something and we're going deeper as we go down). In that case, I would actually expect to see the y axis title also flip to be at the bottom instead of the top. The mirror case from standard I suppose.

So, I'm envisioning something like:

I suppose this means a "bottom" option would be needed along with a "top".

2. When guides(x.sec = "axis"), I think I would personally opt to keep my y axis title in the left-hand margin (though still leave it horizontal and just break it onto as many lines as possible for efficiency). The double-labelled x axis is not functionality I'd personally use much, so it's harder to wrap my head around. Though I suppose, sometimes, labels/titles clip and perhaps they just should do so when people mix-and-match specifications too inelegantly!

3. Here, I think I can say confidently I'd prefer it below the strips (i.e., closer to the graph), as I view the y-axis title information to be more "primal"/"proximal" to the graph's interpretation than strip information. That said, I'd probably personally opt for strips to go on the bottom by default so they function as almost a second-order/nested x axis, so then they and the y-axis title would be in different regions (not helpful when that isn't the default though, I recognize!).

So, I'd probably do:

Not the best example but hopefully gets the point across. Otherwise, I guess I'd be envisioning this:

If the strip backgrounds could be moved up too (I had to suppress them in that last one).

...Yes, definitely a few intersection points here for sure!

[teunbrand]

Thanks for your thoughts on this! I do think it is something that is nice to have, I'm just not quite convinced it belongs in base ggplot2. To my mind, this is the kind of feature an extension package could support. If you don't want to write your own, I think I might find a place for it in ggh4x if you'd like.

[BajczA475]

It might not belong in base ggplot2--that's true! However, FWIW, I have code I adapted from the accepted answer on the SO post linked to above that I think works quite well. I'll paste it here in case it's useful:

#THIS FUNCTION ALLOWS US TO PLUG INTO THE USUAL GGPLOT SYNTAX BY ESSENTIALLY RAISING A FLAG THAT WE WANT TO TRIGGER THE AXIS_SWITCHER METHOD NEXT, WHICH KICKS OFF THE Y AXIS LABELING PROCESS.
y_title_up = function(location = "top") {
  structure(
    list(location = match.arg(location, c("top", "bottom"))),
    class = "axis_switcher"
  )
}

#THIS AMENDS GGPLOT_ADD'S NORMALLY BEHAVIOR TO FIND A PLOT PROVIDED AND APPEND THE CLASS "SWITCHER" TO IT.
ggplot_add.axis_switcher = function(object, plot, name = "switcher") {
  plot$y_axis_switch_location = object$location
  class(plot) = c("switcher", class(plot))
  return(plot)
}

#THIS AMENDS GGPLOT_BUILD'S NORMAL BEHAVIOR TO WATCH FOR A PLOT WITH THE "SWITCHER" CLASS AND, WHEN IT ENCOUNTERS IT, BUILDS IT NORMALLY, THEN APPENDS THE "SWITCHED" CLASS.
ggplot_build.switcher = function(plot) {
  class(plot) = c("gg", "ggplot")
  output = ggplot_build(plot)
  class(output) = c("switched", class(output))
  output
}

#THIS AMENDS GGPLOT_GTABLE'S NORMAL OPERATIONS SUCH THAT, IF A PLOT HAS THE "SWITCHED" CLASS, IT APPENDS A NEW Y AXIS TITLE USING OUR FUNCTION ABOVE.
ggplot_gtable.switched = function(plot) {
  loc = ifelse(!is.null(plot$plot$y_axis_switch_location), 
                plot$plot$y_axis_switch_location,
                "top")
  switch_axis_label(plot$plot, location = loc)
}

#A FUNCTION THAT CAN BE USED IN A TYPICAL + CHAIN TO CREATE A GGPLOT THAT HAS THE Y AXIS TITLE MOVED TO ABOVE THE PLOT, INTO A TEXTGROB THAT NORMALLY HOUSES TOP X AXIS INFO AND OTHERWISE HAS A HEIGHT OF 0. 
switch_axis_label = function(p, location = "top") {
  
  lab = p$scales$get_scales("y")$name #GET THE Y AXIS TITLE STRING PROVIDED TO ANY SCALE_Y_ FUNCTION FIRST.
  if(is.null(lab)) {
    lab = p$labels$y #OTHERWISE, GRAB THE DEFAULT Y LABEL FROM THE ORIGINAL DATA COLUMN'S NAME.
  }

  #IF YOU'VE SPECIFIED A NEW Y SCALE TITLE VALUE VIA A SCALE_Y_ FUNCTION, THIS NUKES IT. 
  if(!is.null(p$scales$get_scales("y"))) {
    y = which(unlist(lapply(p$scales$scales, function(x) { "y" %in% x$aesthetics } )))
    p$scales$scales[[y]]$name = NULL
  }
  
  #THIS ALSO NUKES THE DEFAULT Y AXIS TITLE STRING.
  p = p + labs(y = NULL)
  
  #NOW, WE CONVERT THE GGPLOT WE ALREADY HAVE INTO A GTABLE.
  gt = p %>%  ggplot_build() %>% ggplot_gtable()
  
  #HERE, WE ATTEMPT TO PORT OVER ANY THEME-RELATED ADJUSTMENTS TO THE APPEARANCE OF THE Y AXIS TITLE.
  element = calc_element("axis.title.y", p$theme) #GRAB THE ELEMENT'S CURRENT THEME CHARACTERISTICS

  #NOT ALL THEME CHARACTERISTICS HAVE THE SAME NAME WITH GROBS, SO THIS TRANSLATES.
  translate_element = function(el) {
    el_list = as.list(el)
    # Translate key names
    if (!is.null(el_list$colour)){ el_list$col = el_list$colour }
    if (!is.null(el_list$face)){ el_list$fontface = el_list$face }
    if (!is.null(el_list$size)){ el_list$fontsize = el_list$size }
    
    return(el_list)
  }
  
  #THIS FUNCTION MATCHES UP GROB CHARACTERISTICS WITH THEME ONES WHERE APPROPRIATE.
  element_to_gpar = function(el) {
    el_list = translate_element(el)
    gpar_args = c("col", "fill", "alpha", "lty", "lwd", "lex", "lineend",
                   "linejoin", "linemitre", "fontsize", "cex", "fontfamily",
                   "fontface", "font", "lineheight")
    do.call(grid::gpar, el_list[intersect(names(el_list), gpar_args)])
  }

  #USUALLY, WE TARGET ROW [8,6] BUT CAN INSTEAD TARGET [11,6] IF THE USER WANTS AND WE LACK A BOTTOM X AXIS LABEL ROW.
  target_row = ifelse(location == "bottom", 11, 8)
  
  #SPECIFICALLY TARGET CELL [X, 6] IN THE GTABLE, WHICH IS NORMALLY A SPACER AND SOMETIMES IS JUST NOTHING AND STICK THE NEW TITLE THERE. THIS WILL CLIP OVERTOP OF THE X AXIS LABELS FOR A TOP X AXIS, BUT THAT'S AN EDGE CASE THAT WOULDN'T BE DESIRABLE ANYHOW.
  idx = which(gt$layout$t <= target_row & gt$layout$b >= target_row &
                gt$layout$l <= 6 & gt$layout$r >= 6) #FIND ANY GROBS OCCUPYING CELL [X, 6].
  #IF THERE IS NO GROB THERE, OR IT'S JUST A SPACER OR THE BACKGROUND, WE CAN SAFELY MOVE THE Y AXIS TITLE TO THAT CELL.
  if (length(idx) == 0 || all(is.na(gt$layout$name[idx])) || all(gt$layout$name[idx] %in% c("spacer", "background"))) {
    gt = gtable::gtable_add_grob(
      gt,
      grob = grid::textGrob(lab, 
                            x = 0, 
                            y = 0.5, 
                            hjust = 0, #NOT IDEAL FOR IT TO BE HARDCODED BUT W/E
                            vjust = ifelse(element$vjust, element$vjust, 0.5),
                            rot = 0, #THIS IS THE WHOLE POINT!
                            gp = element_to_gpar(element)), #TRANSLATE IN THEME CHARACTERISTICS TO THE GROB.
      t = target_row,
      l = 6, 
      name = "custom-y-title", 
      clip = "off"
    )
  }
  
  #MAKE ROW 8/11 HAVE A NON-ZERO HEIGHT (THIS IS THE ROW THAT SECOND GTABLE GROB WOULD NORMALLY GO IN--IT HAS A 0 HEIGHT UNLESS A TOP X-AXIS EXISTS.)
  gt$heights[target_row] = grid::unit(1.5, "lines") #=-FOR ME, 2 LINES SEEMS ENOUGH SPACE.
  #WARNINGS REGIONS ------
  
  #WARNING #1--IF USERS HAVE MOVED THE X AXIS TO THE TOP OR HAVE DUPLICATED IT THERE, THE NEW Y AXIS TITLE WILL LIKELY CLIP THE LABELS
  axis_t_rows = which(grepl("^axis-t", gt$layout$name)) #FIND AXIS-T GROBS.
  axis_t_grobs = gt$grobs[axis_t_rows] #PULL THEM OUT
  
  #SEE IF ANY OF THESE GROBS FAIL TO INHERIT THE ZEROGROB CLASS, WHICH THEY GET IF THEY ARE ACTUALLY EMPTY. 
  x_axis_top_visible = any(!vapply(axis_t_grobs, inherits, what = "zeroGrob", logical(1)))
  
  #IF ANY DO FAIL TO INHERIT, THEN WE WARN THE USER.
  if (x_axis_top_visible & location == "top") {
    warning("Heads-up: The top y axis title is likely to clip overtop of the x axis labels if your graph features a top x axis. Move the x axis to the bottom using \"position = 'top'\" in scale_x_*() (or remove the secondary x axis). Alternatively, set \"location = 'bottom'\" in switch_y_axis(). ")
  }
  
  #WARNING #2--IF USERS HAVE FACETED AND HAVE FACET STRIPS AT THE TOP POSITION, THE NEW Y AXIS TITLE WILL GO ABOVE RATHER THAN BELOW THEM. IN THIS CASE, I'D ADVISE MOVING THEM TO THE BOTTOM OF THE GRAPH INSTEAD.
  strip_t_rows = which(grepl("^strip-t", gt$layout$name)) #FIND ANY STRIP-T GROBS.
  strip_t_grobs = gt$grobs[strip_t_rows] #PULL THEM OUT
  
  #SEE IF ANY OF THESE GROBS FAIL TO INHERIT THE ZEROGROB CLASS, WHICH THEY GET IF THEY ARE ACTUALLY EMPTY. 
  top_strips = any(!vapply(strip_t_grobs, inherits, what = "zeroGrob", logical(1)))
  
  #IF ANY DO FAIL TO INHERIT, THEN WE WARN THE USER.
  if (top_strips) {
    warning("Heads-up: The top y axis title will be placed above any top strip labels on faceted graphs. This may not be ideal; in these instances, I recommend moving your top facet strips to the bottom. In facet_*(), specify \"strip.position = 'bottom'\" to do this.")
  }
  
  # END WARNINGS ----
  
  grid::grid.draw(gt) #DRAW THE NEW GTABLE (PLOT) (HAS TO BE LAST!)
  
}

Full disclosure: I do use ChatGPT to troubleshoot/tinker, so some of this code is likely from ChatGPT but I verified and annotated it line by line--so far as I can tell, it is doing what it says on the tin :). But I'm no expert!