[R] How to open more windows to make more graphs at once!

[Faramarzi Monireh]

Dear R users,
I have a data frame (test) including five columns of upper (numeric), lower (numeric), observed (numeric), best_sim (numeric) and stname (factor with 80 levels, each level with different length). Now I would like to write a short program to draw one graph as follow for each level of stname but I would like also to draw each time 12 graphs for the 12 levels of stname in the same graphic windows and save it as "jpeg' file . This means at the end I will have 7 (80 levels/12=7) graphic windows and 7 jpeg files each one with 12 graphs (the last one with 8 graphs) for the 12 levels of stname. I already wrote the following script to do it each time for 12 levels of stname but I have to change script each time for the another 12 levels [line 3 in the script for example: for( i in levels(test$stname)[12:24))] and I do not know how can I save the obtained graphs (seven graphic windows) as jpeg files (e.g. plot1.jpeg, plot2.jpeg and so on). As I have 45 dataset like this it would be great if somebody can help me to complete this script to do all together for a dataset using a script.
Thank you very much in advance for your cooperation,
Monireh


      
windows(9,9)
par(mfrow = c(3,4))
for( i in levels(test$stname)[1:12])
{ 
data<- test[test$stname==i,]
xx <- c(1:length(data$upper), length(data$upper):1)
yy <- c(data$upper, rev(data$lower))
zz<- data$observed
tt<- data$Best_Sim
par(lab =c(10,15,2))
plot.jpeg<- plot(xx,yy, type="n", xlim=c(min(xx), max(xx)), ylim=c(min(zz,yy,tt), max(yy,zz,tt)*1.4),
 main= i, xlab="Month (1990-2002)",  ylab="Discharge(m3/s)", font.axis=6)
polygon(xx, yy, col="green",  border = "NA")
lines(zz, col="blue", lwd=1.5)
lines(tt,col="red", lwd=1.5) 
legend(length(zz)-60, max(yy,zz,tt)*1.45, c("Upper Limit", "Lower Limit", " Observed","Best etimation")
, lwd=c(10, 1,1.7,1.7), bty="n", col= c("green", "white", "blue","red"))
 }