Is it possible to split axis labels into two lines in the base graph?

Question

I am trying to split the labels on the x axis into two lines. I would also like the labels to be rotated 45 degrees. How can i do this?

What I still have:

N <- 10
dnow <- data.frame(x=1:N, y=runif(N), labels=paste("This is observation ",1:N))
with(dnow, plot(x,y, xaxt="n", xlab=""))
atn <- seq(1,N,3)
axis(1, at=atn, labels=labels[atn])

Answer 1

Here is one opportunity with the package ggplot2.

N <- 10
labs <- factor(1:N,labels=paste("This is \n observation",1:N))
dnow <- data.frame(x=1:N, y=runif(N), labels=labs)
qplot(labels,y,data=dnow) + 
      opts(axis.text.x=theme_text(angle=-45,hjust=0))

I look forward to seeing examples of basic packages!

Answer 2

This is what I prepared (before my ggplot2days) using the basic graphics:

## data
N <- 10
dnow <- data.frame(x=1:N, y=runif(N), labels=paste("This is \nobservation ",1:N))
## make margins wide
par(mfrow=c(1,1), mar=c(10,10,6,4))
## plot without axix labels or ticks
with(dnow, plot(x,y, xaxt="n", xlab=""))
## the positions we ant to plot
atn <- seq(1,N,3)
## the label for these positions
lab <- dnow$labels[atn]
## plot the axis, but do not plot labels
axis(1, at=atn, labels=FALSE)
## plot labels
text(atn, ## x position
     par("usr")[3]-.05, ## position of the low axis
     srt=45, ## angle
     labels=lab, ##labels
     xpd=TRUE, ## allows plotting outside the region 
     pos=2)
## par("usr")[3]