[R] Time Series in R with ggplot2

[info at mathewanalytics.com]

Hi Folks,

First, the important information.

> sessionInfo()
R version 2.12.1 (2010-12-16)
Platform: i386-pc-mingw32/i386 (32-bit)

Second, my problem.

I have a series of data sets comprised in the following format.

> totsoc
   Location Year Value
1     SOUTH 1998    29
2     SOUTH 1999    20
3     SOUTH 2000    32
4     SOUTH 2001    29
5     SOUTH 2002    25
6     SOUTH 2003    28
7     SOUTH 2004    27
8     SOUTH 2005    28
9     SOUTH 2006    22
10    SOUTH 2007    31

In order to generate a time series plot in ggplot2, I ran the following
code.

qplot(Year, Value, data=totsoc, geom="line")

ggplot(totsoc, aes(x=Year, y=Value)) + geom_line()

However, neither command acctually produces a plot with lines connecting
the 
data points. I get a blank window with the general gray background and the
x 
and y axis. The strange thing is that ggplot2 gives me the appropriate
output
when I use "bar" or "point". For example, these commands work.

ggplot(totsoc, aes(Year, Value)) + geom_point()

qplot(Year, Value, data=totsoc, geom="point")

I also tried to generate some sample data, and that worked. However,
I'm not sure why these same commands aren't working on the earlier data
set.
Here is the sample data I was working with.

df <- data.frame(one=c(3,8,5,4,2), two=c("KS","MO","KS","CA","IA"),
three=c(2001:2005))
qplot(three, one, data=df, geom="line")


Can anyone please help?

Thank You,
A. Mathew