How to add a ggplot2 subtitle with different size and colour?

Question

I'm using ggplot2 to improve precipitation barplots.

Here's a reproducible example of what I want to achieve:

library(ggplot2) library(gridExtra) secu <- seq(1, 16, by=2) melt.d <- data.frame(y=secu, x=LETTERS[1:8]) m <- ggplot(melt.d, aes(x=x, y=y)) +   geom_bar(fill="darkblue") +    labs(x="Weather    stations", y="Accumulated Rainfall [mm]") +   opts(axis.text.x=theme_text(angle=-45, hjust=0, vjust=1),        title=expression("Rainfall"), plot.margin = unit(c(1.5, 1, 1, 1), "cm"),        plot.title = theme_text(size = 25, face = "bold", colour = "black", vjust = 5)) z <- arrangeGrob(m, sub = textGrob("Location", x = 0, hjust = -3.5, vjust = -33, gp = gpar(fontsize = 18, col = "gray40"))) #Or guessing x and y with just option z 

I don't know how to avoid using guessing numbers on hjust and vjust on ggplot2? Is there a better way to put a subtitle (not just using \n, but a subtitle with different text color and size)?

I need to be able to use with ggsave to have a pdf file.

Here are two related questions:

Add a footnote citation outside of plot area in R?

How can I add a subtitle and change the font size of ggplot plots in R?

Thanks for any help.

Answer 1

The latest ggplot2 builds (i.e., 2.1.0.9000 or newer) have subtitles and below-plot captions as built-in functionality. That means you can do this:

library(ggplot2) # 2.1.0.9000+   secu <- seq(1, 16, by=2) melt.d <- data.frame(y=secu, x=LETTERS[1:8])  m <-  ggplot(melt.d, aes(x=x, y=y)) m <- m + geom_bar(fill="darkblue", stat="identity") m <- m + labs(x="Weather    stations",                y="Accumulated Rainfall [mm]",               title="Rainfall",               subtitle="Location") m <- m + theme(axis.text.x=element_text(angle=-45, hjust=0, vjust=1))  m <- m + theme(plot.title=element_text(size=25, hjust=0.5, face="bold", colour="maroon", vjust=-1)) m <- m + theme(plot.subtitle=element_text(size=18, hjust=0.5, face="italic", color="black")) m 

Answer 2

Ignore this answer ggplot2 version 2.2.0 has title and subtitle functionality. See @hrbrmstr's answer below.

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You could use nested atop functions inside an expression to get different sizes.

EDIT Updated code for ggplot2 0.9.3

m <-  ggplot(melt.d, aes(x=x, y=y)) +       geom_bar(fill="darkblue", stat = "identity") +       labs(x="Weather    stations", y="Accumulated Rainfall [mm]") +       ggtitle(expression(atop("Rainfall", atop(italic("Location"), "")))) +      theme(axis.text.x = element_text(angle=-45, hjust=0, vjust=1),       #plot.margin = unit(c(1.5, 1, 1, 1), "cm"),       plot.title = element_text(size = 25, face = "bold", colour = "black", vjust = -1))