Invoke R Language/script from java

Question

How do we invoke R language / R script from java? Basically I need java kind of wrapper around R script.

1. Data will be given to java layer say method setData(double[]) which should in turn sends to R script - let us say setDataR(double []) method.

2. R script will perform some computation say calls method double[] computeR().

3. Java program will get the computation result by invoking double[] getData() which in turn delegates to R script to get the computated data.

How can this be performed by JRI, Rserv, Rcaller? I do not see any way to invoke Rscript methods? Please send sample. It should be simular to JNI (java, C++) invocations.

1. Does within jvm I think multiple threads cannot invoke R script call correct? Any work around?

Thanks

Answer 1

RCaller exactly does what you want. Suppose you have a double array 'a' that is defined as

double[] a = new double[] {1.0, 2.0, 3.0};

and you want to calculate the mean, median and standard deviation values. Create a new instance of RCaller

RCaller caller = new RCaller();
Globals.detect_current_rscript();
caller.setRscriptExecutable(Globals.Rscript_current);

RCode code = new RCode();


code.addDoubleMatrix("a", a);
code.addRCode("s <- list(mean=mean(a), median=median(a), sd=sd(a))");

caller.setRCode(code);

caller.runAndReturnResult("s");

double mean = caller.getParser().getAsDoubleArray("mean")[0];
double median = caller.getParser().getAsDoubleArray("median")[0];
double sd = caller.getParser().getAsDoubleArray("sd")[0];

and the variable median holds the value of 2.0 which is returned from the R script. For details visit the page here

Answer 2

The most simple way to use R from Java is using Runtime.exec(""), grabbing the response and parsing it. A typical example on how to run native instructions would be:

Process p = Runtime.getRuntime().exec("ls");
BufferedReader stdInput = new BufferedReader(new InputStreamReader(p.getInputStream()));
BufferedReader stdError = new BufferedReader(new InputStreamReader(p.getErrorStream()));

From here, you can read and process the result printed to the standard output being buffered into stdInput.