Aligning title, subtitle and caption for horizontal ggplot barchart

This question refers to this github tidyverse/ggplot2 solved issue: https://github.com/tidyverse/ggplot2/issues/3252

And it is implemented in ggplot2 (development version): https://github.com/tidyverse/ggplot2/blob/15263f7580d6b5100989f7c1da5d2f5255e480f9/NEWS.md

Themes have gained two new parameters, plot.title.position and plot.caption.position, that can be used to customize how plot title/subtitle and plot caption are positioned relative to the overall plot (@clauswilke, #3252).

To follow your example as a reprex:

# First install the development version from GitHub:
#install.packages("devtools") #If required
#devtools::install_github("tidyverse/ggplot2")

library(ggplot2)
packageVersion("ggplot2")
#> [1] '3.2.1.9000'

df <- data.frame(type=factor(c("Brooklyn","Manhatten and\n Queens")),
                 value=c(15,30))

ggplot(df, aes(x=type, y=value)) +
  geom_bar(stat='identity') +
  coord_flip() +
  labs(title = "This is a nice title",
       subtitle = "A subtitle",
       caption  = "We even have a caption. A very long one indeed.") +
  theme(plot.caption = element_text(hjust = 0, face= "italic"), #Default is hjust=1
        plot.title.position = "plot", #NEW parameter. Apply for subtitle too.
        plot.caption.position =  "plot") #NEW parameter

^{Created on 2019-09-04 by the reprex package (v0.3.0)}

While you could edit those three grobs, you can also just:

library(gridExtra)
library(grid)

grid.arrange(
  textGrob("This is a nice title", 
           gp=gpar(fontsize=16, col="#2b2b2b"), 
           x=unit(0.005, "npc"), just=c("left", "bottom")),
  textGrob("A subtitle",  
           gp=gpar(fontsize=12, col="#2b2b2b"), 
           x=unit(0.005, "npc"), just=c("left", "bottom")),
  ggplot(df, aes(x=type, y=value)) +
    geom_bar(stat='identity') +
    coord_flip() +
    theme(axis.title=element_blank()),
  textGrob("We even have a caption. A very long one indeed.", 
           gp=gpar(fontsize=9, col="#2b2b2b"), 
           x=unit(0.005, "npc"), just=c("left", "bottom")),
  ncol=1,
  heights=c(0.075, 0.025, 0.85, 0.05)
)

Make a wrapper for it, put it in a personal pkg. Boom. Done.

---

library(ggplot2)
library(gridExtra)
library(grid)

df <- data.frame(type=factor(c("Brooklyn","Manhatten and\n Queens")), value=c(15,30))

ggplot(df, aes(x=type, y=value)) +
  geom_bar(stat='identity') +
  coord_flip() +
  theme(axis.title=element_blank()) +
  theme(plot.margin=margin(l=0, t=5, b=5))-> gg

flush_plot <- function(x, title, subtitle, caption) {
  tg <- function(label, ...) {
    textGrob(label,  x=unit(0, "npc"), just=c("left", "bottom"),
             gp=do.call(gpar, as.list(substitute(list(...)))[-1L])) }
  grid.arrange(
    tg(title, fontsize=16, col="#2b2b2b"),
    tg(subtitle, fontsize=12, col="#2b2b2b"), x,
    tg(caption, fontsize=9, col="#2b2b2b"),
    ncol=1, heights=c(0.075, 0.025, 0.85, 0.05)
  )
}

flush_plot(gg, "This is a nice title", "A subtitle", 
           "We even have a caption. A very long one indeed.")