R from within Java

Question

What's the best way to call R functionality from within Java?

I'm looking for a quick, easy and reliable way to make standard 2d scatter plots and histograms in R using my Java applications. I was wondering which packages/interfaces that came up in a quick Google search would be most convenient to use.

I look forward to your suggestions!

Answer 1

Use JRI: http://www.rforge.net/JRI/. It comes bundled with rJava, including some examples of usage.

A very simple example would be like this:

import java.io.*;
import java.awt.Frame;
import java.util.Enumeration;

import org.rosuda.JRI.Rengine;
import org.rosuda.JRI.REXP;
import org.rosuda.JRI.RVector;
import org.rosuda.JRI.RMainLoopCallbacks;

public class rJavaTest {

    public static void main(String[] args) {

        Rengine re=new Rengine(args, false, new TextConsole());
        REXP x;
        re.eval("print(1:10/3)");
        System.out.println(x=re.eval("iris"));
        RVector v = x.asVector();
        if (v.getNames()!=null) {
            System.out.println("has names:");
            for (Enumeration e = v.getNames().elements() ; e.hasMoreElements() ;) {
                System.out.println(e.nextElement());
            }
        }

        if (true) {
            System.out.println("Now the console is yours ... have fun");
            re.startMainLoop();
        } else {
            re.end();
            System.out.println("end");
        }
    }
}

Answer 2

There is something new called http://www.renjin.org/

One thing i like it over JRI is deployment, While jri required that your application users will download R, renjin does not, and it uses only the JVM to run.

Answer 3

I have found that forking R as a process, attaching to the process's stdin, stdout, and stderr streams, and sending R commands via the input stream to be quite effective. I use the filesystem to communicate between R and my Java process. This way, I can have multiple R processes running from different threads in Java and their environments do not conflict with each other.

Answer 4

FastR is a GraalVM based implementation of R. Embedding it in a JVM application is as simple as:

Context ctx = Context.newBuilder("R").allowAllAccess(true).build();
ctx.eval("R", "sum").execute(new int[] {1,2,3});

For your concrete example, this example plots a scatter plot using the lattice R package, but the output is drawn into Graphics2D object.

    Context context = Context.newBuilder("R").allowAllAccess(true).build();
    // This R function opens FastR graphics device passing it Graphics2D object,
    // then it plots the graph and closes the device
    String src =
        "library(grid); library(lattice); " +
        "function(graphics, width, height, x, y) { " +
        "   awt(width, height, graphics);" +
        "   print(xyplot(as.vector(x) ~ as.vector(y)));" +
        "   dev.off();" +
        "}";
    Value showPlot = context.eval("R", src);

    // Create a BufferedImage to use for the plotting
    BufferedImage image = new BufferedImage(WIDTH, HEIGHT, TYPE_INT_RGB);
    Graphics2D graphics = (Graphics2D) image.getGraphics();
    graphics.setBackground(new Color(255, 255, 255));
    graphics.clearRect(0, 0, WIDTH, HEIGHT);

    // Invoke R plotting code and pass it graphics object
    double[] x = new double[] {1.,2.,3.,4.};
    double[] y = new double[] {1.,2.,3.,4.};
    showPlot.execute(graphics, WIDTH, HEIGHT, x, y);

There is also an example that shows the plots inside a Swing window.

You can find more details about FastR in this medium post: https://medium.com/graalvm/faster-r-with-fastr-4b8db0e0dceb