ggplot2: Creating themed title, subtitle with cowplot

Question

I have a list of data frames that I use to make a list of ggplots, and then assemble into a grid of plots with cowplot. I need to then attach a sha

Answer 1

Like so?

library(ggplot2)
library(cowplot)

theme_georgia <- function(...) {
  theme_gray(base_family = "Georgia", ...) + 
    theme(plot.title = element_text(face = "bold"))
}


title_theme <- calc_element("plot.title", theme_georgia())

ggdraw() + 
  draw_label(
    "Socio-economic measures",
    fontfamily = title_theme$family,
    fontface = title_theme$face,
    size = title_theme$size
  )

Created on 2018-06-21 by the reprex package (v0.2.0).

Answer 2

@Claus Wilke's solution got the job done, but I was inspired to write a wrapper function around draw_label to get the styling necessary to mimic a theme element. I'm posting here in case it's of use to anybody else, though this might be a weird use case.

This function takes a theme function or, if theme is omitted, gets the current theme from theme_get. It also takes the name of a theme element, such as "plot.title", from which it gets the styling with calc_element. All the requisite arguments are passed to cowplot::draw_label, along with anything else in ... such as x or hjust.

library(tidyverse)
library(cowplot)

draw_label_theme <- function(label, theme = NULL, element = "text", ...) {
  if (is.null(theme)) {
    theme <- ggplot2::theme_get()
  }
  if (!element %in% names(theme)) {
    stop("Element must be a valid ggplot theme element name")
  }

  elements <- ggplot2::calc_element(element, theme)

  cowplot::draw_label(label, 
                      fontfamily = elements$family,
                      fontface = elements$face,
                      colour = elements$color,
                      size = elements$size,
                      ...
  )
}

title <- ggdraw() +
  draw_label_theme("Socio-economic measures", 
                   theme = theme_georgia(), element = "plot.title",
                   x = 0.05, hjust = 0, vjust = 1)
subtitle <- ggdraw() +
  draw_label_theme("By census tract, 2016",
                   theme = theme_georgia(), element = "plot.subtitle",
                   x = 0.05, hjust = 0, vjust = 1)

Now the only hard part is lining things up neatly in the rel_heights, which I could mess around with more here. There might be positioning information to pull out of the theme and use to set the heights.

plot_grid(title, subtitle, gridded, ncol = 1, rel_heights = c(0.1, 0.1, 1))