R help - Apr 2009 - Plotting C++ output in R

Hi,

Using R 2.8.0 on Windows,

I have a mathematical model written in C++, the model writes to file (.txt) a
set of numbers I want to plot in R.
The model iterates over about 10,000 runs, each time overwriting  the old with
the new set of results to the output file.

I want to be able to continuously plot the output from the model in R each time
a new run generates data.

At the moment I tried cheating a little by creating a continuous loop which
constantly scans another output file from the model which contains the current
run number, when the run number changes, R then goes on to plot  the new C++
output.

The 'Quick' code I tried which works to a certain extent, although very
bad idea I am sure,
The idea is I strt R first and then run the C++ Model

#Make sure the C++ run number output file is zeroed
write.table(0, file = "C://rdata//Outfile5.txt",quote = F, row.names =
F,col.names = F)
 
#Set up legend and colors
leg.txt<-c("Male Younger", "Male Older", "Female
Younger", "Female Older")
leg.cols<-c("cyan","blue","pink","magenta")

#The number of runs for the C++ model
runs=10000 

#Loop corresponding to the number of runs in the C++ model
for(i in 1:runs){ 
# set / reset the plot variable to 0 (no plotting)
			plot<-0 
#read the current run number from the C++ model
			nogo<-read.table("c:\\rdata\\Outfile5.txt",header=F)
#This loop tries to implement a continuous scan of the C++ output file
containing the current run number
          		for(i in 1:1000){ 
# Reads the current run number from the C++ file
  						go<-read.table("c:\\rdata\\Outfile5.txt",header=F) 
 #Tried to make a continuous loop by reseting i from the for loop to 1 again
(which doesnt work)
						i<-1
#Pause the whole thing for a while
						Sys.sleep(0.2) 
# If the C++ model run number has been updated
						if(go==nogo+1)
						{
# Set the I from the for loop to max so we get an exit
							i<-1000
# set plot variable to 1 (Plot)
							plot<-1 
						}
					}
#If the plot variable is one indicating plot the data
		if(plot==1){ 
#read the C++ model output for this run
				data<-read.table("c:\\rdata\\Outfile3.txt") 
#Plot the data				
			
plot(data[1:41,2],data[1:41,3],type="l",ylim=c(0,0.3),col="cyan",xlab="Years",ylab="Proportion
HIV Infected",lwd=2)
				legend(x=0,y=0.08,leg.txt,fill = leg.cols)
				lines(data[1:41,2],data[1:41,4],col="blue",lwd=2)
				lines(data[1:41,2],data[1:41,5],col="pink",lwd=2)
				lines(data[1:41,2],data[1:41,6],col="magenta",lwd=2)

				}

		}




Hope I am making sense in my question (If not in my code).

Any help welcome.

Many thanks

Andrew Paul Cox
Mathematical Modeller
London School of Hygiene and Tropical Medicine
WC1E 7HT

Andrew.Cox at lshtm.ac.uk wrote:
> 
> I want to be able to continuously plot the output from the model in R
> each time a new run generates data.
 From the C++ program, run the R script that plots the data.  Something 
like this:

	system("Rscript myplotter.R");

That assumes Rscript is in the PATH, and that it works on Windows.  I'll 
assume you can figure out the details.

You might also consider making the C++ program write the R script, so 
bits can vary.  For instance, each iteration of the model could write 
out to a different data file, then call R from a new thread, so the R 
analysis stage doesn't interfere with the generation of the next 
iteration's results.  Remove the now-unwanted data file when system() 
returns, and end the thread.