Skip navigation

ggplot2で字幕
[Subtitles in ggplot2]

UPDATE: A newer blog post explaining the new ggplot2 additions: http://rud.is/b/2016/03/16/supreme-annotations/

UPDATE: this capability (+ more) are being rolled into ggplot2-proper. PR will be absorbed into ggplot2 main branch soon. exciting, annotated times ahead!

UPDATE: fontsize issue has been fixed & there’s a Shiny gadget available for interactively making subtitles. More info at the end of the post.

Subtitles aren’t always necessary for plots, but I began to use them enough that I whipped up a function for ggplot2 that does a decent job adding a subtitle to a finished plot object. More than a few folks have tried their hand at this in the past and this is just my incremental contribution until there’s proper support in ggplot2 (someone’s bound to add it via PR at some point).

We’ll nigh fully recreate the following plot from this WaPo article:

2300lawyers0116-2

Here’s a stab at that w/o the subtitle:

library(ggplot2)
library(scales)
 
data.frame(
  yrs=c("1789-90", "1849-50", "1909-10", "1965-66", "2016-16"),
  pct=c(0.526, 0.795, 0.713, 0.575, 0.365),
  xtralabs=c("", "Highest:\n", "", "", "Lowest:\n")
) -> hill_lawyers
 
gg <- ggplot(hill_lawyers, aes(yrs, pct))
gg <- gg + geom_bar(stat="identity", width=0.65)
gg <- gg + geom_label(aes(label=sprintf("%s%s", xtralabs, percent(pct))),
                      vjust=-0.4, family=c(rep("FranklinGothic-Book", 4),"FranklinGothic-Heavy"), 
                      lineheight=0.9, size=4, label.size=0)
gg <- gg + scale_x_discrete()
gg <- gg + scale_y_continuous(expand=c(0,0), limits=c(0.0, 1.0), labels=percent)
gg <- gg + labs(x=NULL, y=NULL, title="Fewer and fewer lawyers on the Hill")
gg <- gg + theme_minimal(base_family="FranklinGothic-Book")
gg <- gg + theme(axis.line=element_line(color="#2b2b2b", size=0.5))
gg <- gg + theme(axis.line.y=element_blank())
gg <- gg + theme(axis.text.x=element_text(family=c(rep("FranklinGothic-Book", 4),
                                                   "FranklinGothic-Heavy")))
gg <- gg + theme(panel.grid.major.x=element_blank())
gg <- gg + theme(panel.grid.major.y=element_line(color="#b2b2b2", size=0.1))
gg <- gg + theme(panel.grid.minor.y=element_blank())
gg <- gg + theme(plot.title=element_text(hjust=0, 
                                         family="FranklinGothic-Heavy", 
                                         margin=margin(b=10)))
gg

RStudio

(There are some “tricks” in that plotting code that may be worth spending an extra minute or two to mull over if you didn’t realize some of the function parameters were vectorized, or that you could get a white background with no border for text labels so grid lines don’t get in the way.)

Ideally, a subtitle would be part of the gtable that gets made underneath the covers so it will “travel well” with the plot object itself. The function below makes a textGrob from whatever text we pass into it and does just that; it inserts the new grob into a new table row.

#' Add a subtitle to a ggplot object and draw plot on current graphics device.
#' 
#' @param gg ggplot2 object
#' @param label subtitle label
#' @param fontfamily font family to use. The function doesn't pull any font 
#'        information from \code{gg} so you should consider specifying fonts
#'        for the plot itself and here. Or send me code to make this smarter :-)
#' @param fontsize font size
#' @param hjust,vjust horizontal/vertical justification 
#' @param bottom_margin space between bottom of subtitle and plot (code{pts})
#' @param newpage draw new (empty) page first?
#' @param vp viewport to draw plot in
#' @param ... parameters passed to \code{gpar} in call to \code{textGrob}
#' @return Invisibly returns the result of \code{\link{ggplot_build}}, which
#'   is a list with components that contain the plot itself, the data,
#'   information about the scales, panels etc.
ggplot_with_subtitle <- function(gg, 
                                 label="", 
                                 fontfamily=NULL,
                                 fontsize=10,
                                 hjust=0, vjust=0, 
                                 bottom_margin=5.5,
                                 newpage=is.null(vp),
                                 vp=NULL,
                                 ...) {
 
  if (is.null(fontfamily)) {
    gpr <- gpar(fontsize=fontsize, ...)
  } else {
    gpr <- gpar(fontfamily=fontfamily, fontsize=fontsize, ...)
  }
 
  subtitle <- textGrob(label, x=unit(hjust, "npc"), y=unit(hjust, "npc"), 
                       hjust=hjust, vjust=vjust,
                       gp=gpr)
 
  data <- ggplot_build(gg)
 
  gt <- ggplot_gtable(data)
  gt <- gtable_add_rows(gt, grobHeight(subtitle), 2)
  gt <- gtable_add_grob(gt, subtitle, 3, 4, 3, 4, 8, "off", "subtitle")
  gt <- gtable_add_rows(gt, grid::unit(bottom_margin, "pt"), 3)
 
  if (newpage) grid.newpage()
 
  if (is.null(vp)) {
    grid.draw(gt)
  } else {
    if (is.character(vp)) seekViewport(vp) else pushViewport(vp)
    grid.draw(gt)
    upViewport()
  }
 
  invisible(data)
 
}

The roxygen comments should give you an idea of how to work with it, and here it is in action:

subtitle <- "The percentage of Congressional members that are laywers has been\ncontinuously dropping since the 1960s"
 
ggplot_with_subtitle(gg, subtitle,
                     fontfamily="FranklinGothic-Book",
                     bottom_margin=20, lineheight=0.9)

Fullscreen_3_12_16__3_39_PM

It deals with long annotations pretty well, too (I strwrapped the source text for the below at 100 characters). The text is senseless here, but it’s just for show (I had it handy…don’t judge…you’re getting free code :-):

Fullscreen_3_12_16__7_44_PM

I think this beats manually re-creating the wheel, even if you only infrequently use subtitles. It definitely beats hand-editing plots and is a bit more elegant and functional than using grid.arrange (et al) to mimic the functionality. It also beats futzing with panel margins and clipping to shoehorn a frankenmashup mess of geom_text or annotation_custom calls.

Kick the tyres, tell me where it breaks and if I can cover enough edge cases (or make it smarter) I’ll add it to my ggalt package.

Shiny Subtitle Gadget

Thanks to:

you can now play with an experimental Shiny gadget which you can load by devtools::install_github("hrbrmstr/hrbrmisc") (that’s a temporary home for it, I use this pkg for testing/playing). Just select a ggplot2 object variable name in RStudio and then select “Add subtitle” from the Addins menu and give it a whirl. It looks like this:

__Development_hrbrmisc_-_master_-_RStudio

10 Comments

  1. Re font information: I use this with add_sub form the cowplot package:

    not_gg <- add_sub(gg, text, [...],
    size=theme_get()$text[["size"]]*0.7, # base size on the normal text size
    fontface="italic")

    Do you think it would be possible to add this to ggplot2 directly? E.g. ala gg + ggsubtitle(....)? Using custom grobs makes the output something else than a ggplot object, so you can’t add on to it afterwards… :-(

    • Hadley’s going to prbly kill me but I’m considering a PR to ggplot2 directly to add a subtitle parameter to labs (and a ggsubtitle function). I just need to finish groking his final gtable build code.

      • the add_sub from cowplot would also be nice :-)

        Maybe it would be possible to “just” add a hook into the ggplot draw process, so that other functions could add a function there, which adds the custom grobs?

        like in

        * build the normal plot (kind of the step where ggplot does the equivalent of `data <- ggplot_build(gg); gt <- ggplot_gtable(data)`
        * for function in gg$addon_functions: function(gt)
        * whatever happens then with the gt thing

        The you could implement the above by adding your own parametrized function to the gg$addon_functions and cowplot could do the same…

        Re fontsize issue: Not sure if you only changed it in the code or also in the blogpost here:

        “`

        ‘ @param fontfamily font family to use. The function doesn’t pull any font

        ‘ information from \code{gg} so you should consider specifying fonts

        ‘ for the plot itself and here. Or send me code to make this smarter :-)

        “`

        This should also be in theme_get()$text

    • Forgot to #ty for the font code suggestion, too :-)

    • This was easier than expected. If you’re a brave soul, give https://github.com/hrbrmstr/ggplot2 a go (ggsubtitle & labs(subtite=...) & theme ops on them work)

      • subtitle, presumably

      • I’d really like that functionality in ggplot2, and I don’t see any reason why it shouldn’t be there. Is there a reason hadley would kill you for that? Is it like a “two y axes”-thing?

        • Oh, PR is coming. Just needs some tweaking. Modifying ggplot2 is a really big deal. Tons of downstream dependencies + lots of folks with code automation that rely on the output being a specific way.

  2. Though I have defined the function “” in global_env, I get the following error:

    Error in ggplotwithsubtitle(p4, subtitle, fontfamily = “FranklinGothic-Book”, :
    could not find function “gtableaddrows”

    I am calling the function as follows:
    ggplotwithsubtitle(p4, subtitle,
    #fontfamily=”FranklinGothic-Book”,
    bottom_margin=20, lineheight=0.9, vp=”vp.1″)

    where I have defined the vp as follows:
    grid.newpage()
    pushViewport(viewport(layout = grid.layout(4, 3),name=”vp.1″))

    • You probably need to update gtable. It’s worked on two independent systems for me, but I run non-dev, but bleeding edge of everything.


2 Trackbacks/Pingbacks

  1. By ggplot2で字幕 [Subtitles in ggplot2] – Mubashir Qasim on 13 Mar 2016 at 10:21 am

    […] article was first published on R – rud.is, and kindly contributed to […]

  2. By Adding a subtitle to ggplot2 – Mubashir Qasim on 14 Mar 2016 at 10:19 pm

    […] out to be very simple to apply. (Note that Bob’s post originally appeared on his own blog, as “Subtitles in ggplot2″.) In order to see if I could create a plot with a subtitle, I went back to some of my own code […]

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.