Latest revision as of 23:22, 9 September 2013

How to call R from a Java program

Using JRI (from RJava)

The RJava package also allows calling Java from R.

Set up

• In R, install the RJava package (necessary?)
• The RJava package includes the JRI.jar, but to get JRIEngine.jar and REngine.jar, go to JRI files download
• Add those 3 jars to your lib directory and classpath
• Make sure the R_HOME environment variable is set
  • Type $R_HOME on the command line to see if it is set and what it is set to
  • In eclipse, you can add environment variables to the run configuration
  • On a mac, add this line to your .profile file (in the root of your user directory, so ~/.profile)

export R_HOME=/Library/Frameworks/R.framework/Resources

• Add the native JRI library to the Java library path (either on the command line call to Java or as a VM argument in the eclipse run configuration)

-Djava.library.path=/Library/Frameworks/R.framework/Resources/library/rJava/jri/

Calling R

Here is a very short example. See the links below and the example directory for more.

public void demoCallR() throws Exception
{
  REngine re = null;
  try
  {
    re = REngine.engineForClass("org.rosuda.REngine.JRI.JRIEngine");

    re.assign("num", new int[] { 1 });
	        
    REXP result = re.parseAndEval("num + 1");
	        
    System.out.println(result.asInteger());
  }
  finally
  {
     if (re != null)
     {
       re.close();
     }
  }
}

Which API to use

Confusingly, there are several API's to use. The recommended one is the high-level org.rosuda.REngine API.

REngine eng = REngine.engineForClass("org.rosuda.REngine.JRI.JRIEngine");  
eng.assign("x", "Peter")

See mailing list posts here and here. Note that this is different than many of the examples in the links below, which all show something like this:

// Start R 
Rengine re = new Rengine(new String[] { "--no-save" }, false, null); //specify '--save', '--no-save' or '--vanilla'

if (!re.waitForR())
{
  System.out.println("Cannot load R");
}
else
 {     
  // print a random number from uniform distribution
  System.out.println(re.eval("runif(1)").asDouble ());
       
   // close R
  re.end();
}

Helpful links

• Example with eclipse
• Data types
• Example calling functions and assigning/returning values
• Setup for multiple IDEs and simple test case
• Where to get files
• Also see the jri/examples directory for the files rtest.java and rtest2.java

Other solutions

• renjin this looks promising, a JVM-based interpreter for R, but still beta
• Rserve more complicated client/server setup, so more useful for lots of processes needing R
• Rcaller very simple, but looks clunky for doing anything more than a few lines in R