multiple lines in ggplot

gistfile1.txt

library(ggplot2)
library(reshape2) # gives you the melt function

d1 <- data.frame(time=1:10, x1=1:10)
d2 <- data.frame(time=1:10, x2=1:10/2)

d <- merge(d1, d2, by='time')

d.molten <- melt(d, id.var='time')

ggplot(d.molten, aes(x=time, y=value, group=variable, colour=variable)) + geom_line()

# the general trick is to get a single data.frame with a column for each series you want to plot, 
# then melt the data.frame, and use the group and colour aes in the call to ggplot.