Dear List:

I am generating a series of plots iteratively using Sweave. In short, a
dataframe is subsetted row by row and variable graphics are created
conditional on the data in each row. In this particular case, this code
ends up generating 17,000 individual plots. 

In some cases, all student data (this is working with student
achievement data) are available and my code below works very well in the
sense that a line connects all points. However, in some cases there are
missing data and I need to modify my code so that lines are connected
through all points even when data are missing.

Here is a snip of relevant code. In the actual program, the data in
stu.vector and avg.vector are obtained from the dataframe as the
programs loops through each row. 

stu.vector<-c(2500, 2510,   NA , 2600)
avg.vector<-c(2635, 2589, 2628, 2685)
x <- c(0,1,2,3)
graph.min <- min(stu.vector,avg.vector ,na.rm=TRUE)-150
graph.max <- max(stu.vector,avg.vector ,na.rm=TRUE)+150
plot(x, stu.vector, ylim=c(graph.min,graph.max),  xlab=" ", ylab="Scaled
Score", xaxt='n', pch=2, col='blue', main="Math Growth Rate")
points(x, avg.vector, pch=1, col='red')
lines(x, stu.vector, lty=1, col='blue')
lines(x, avg.vector, lty=3, col='red')

If the NA did not exist in the object stu.vector then all points would
be connected with lines. However, in some cases data are missing and I
need to connect the data in stu.vector with lines. So in this case, the
line would connect points 1 and 2, and then 2 and 4 even though point 3
is missing. 

Can anyone suggest how I might do this? 

Thanks,
Harold


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