The space above and below the legend using ggplot2

Question

If you look at the charts here ! you can see there is a lot of white space above and below the legend. I wish to reduce the amount of space.

Example code:

library(ggplot2)
library(gridExtra)
library(reshape)
library(plyr)
library(scales)

theme_set(theme_bw())

rows <- 1:nrow(faithful)
data <- cbind(faithful, rows)
molten <- melt(data, id.vars='rows', measure.vars=c('eruptions', 'waiting'))

p <- ggplot() +
    geom_line(data=molten, 
        mapping=aes(x=rows, y=value, group=variable, colour=variable), size=0.8) +
    scale_colour_manual(values=c('red','blue')) +
    opts(title='Title') +
    xlab(NULL) + ylab('Meaningless Numbers') +
    opts(
        legend.position='bottom',
        legend.direction='horizontal',
        legend.title=theme_blank(),
        legend.key=theme_blank(),
        legend.text=theme_text(size=9),
        legend.margin = unit(0, "line"),
        legend.key.height=unit(0.6,"line"),      
        legend.background = theme_rect(colour='white', size=0)
    )

ggsave(p, width=8, height=4, filename='crap.png', dpi=125)

Answer 1

To remove the margins of the legend (negative values reduce the white space even more):

p + theme(legend.margin=margin(t=0, r=0, b=0, l=0, unit="cm"))
p + theme(legend.margin=margin(t=0, r=0, b=-0.5, l=0, unit="cm"))

You can also remove the lower part of the plot margin by specifying negative numbers (but make sure that you don't cut off your legend):

p + theme(plot.margin = unit(x = c(0, 0, -0.2, 0), units = "cm"))

Illustrations: ggplot2, legend on top and margin

Answer 2

Here are two additional options that allow you to shrink the space surround the legend:

p + theme(
      legend.key.height=unit(0, "cm"),      
      plot.margin = unit(c(1,0.5,0,0.5), "lines")
    )

The option plot.margin describes how much space there is around the plot itself. The third argument describes the amount of space below the plot. Setting that to zero helps.