Can't label multi-panel figure in r while using ggplot

Question

Sorry for the possibly simple question. I\'m a programmer, though I rarely deal with graphics, and after tearing my hair out for hours with this problem, it\'s time to get some

Answer 1

You could use ggtitle and theme:

df = data.frame(gp = factor(rep(letters[1:3], each = 10)), y = rnorm(30))
p = ggplot(df) + geom_point(aes(x = gp, y = y)) + ggtitle('a') + theme(plot.title=element_text(hjust=0))
p2 = ggplot(df) + geom_point(aes(x = y, y = gp)) + ggtitle('b') + theme(plot.title=element_text(hjust=0))
grid.arrange(p, p2, ncol = 2)

Answer 2

Two (less than ideal) options:

#Use faceting, similar to Matthew's ggtitle option
df = data.frame(gp = factor(rep(letters[1:3], each = 10)), y = rnorm(30))
df$lab1 <- 'a'
df$lab2 <- 'b'
p = ggplot(df) + geom_point(aes(x = gp, y = y)) + facet_wrap(~lab1)
p2 = ggplot(df) + geom_point(aes(x = y, y = gp)) + facet_wrap(~lab2)
j <- theme(strip.text = element_text(hjust = 0.05))
grid.arrange(p + j, p2 + j, ncol = 2)


#Use grid.text
grid.text(letters[1:2],x = c(0.09,0.59),y = 0.99)

For the grid.text option, if you delve into the ggplot object you can probably avoid having to tinker to get those values right manually.