3.3. Evaluating R Language Code

The best way to call R from Java is to use the javax.scripting interfaces. These interfaces are mature and guaranteed to be stable regardless of how Renjin’s internals evolve.

You can create a new instance of a Renjin ScriptEngine using the RenjinScriptEngineFactory class and then instantiate Renjin’s ScriptEngine using the factory’s getEngine() method.

The following code provides a template for a simple Java application that can be used for all the examples in this guide.

import javax.script.*;
import org.renjin.script.*;

// ... add additional imports here ...

public class TryRenjin {
  public static void main(String[] args) throws Exception {
    // create a script engine manager:
    RenjinScriptEngineFactory factory = new RenjinScriptEngineFactory();
    // create a Renjin engine:
    ScriptEngine engine = factory.getScriptEngine();

    // ... put your Java code here ...


We recommend using RenjinScriptEngineFactory directly, as the standard javax.script silently returns null and hides any exceptions encountered when loading Renjin, making it very difficult to debug any project setup problems.

If you’re using Renjin in a more generic context, you can load the engine by name by calling ScriptEngineManager.getEngineByName("Renjin").

With the ScriptEngine instance in hand, you can now evaluate R language source code, either from a String, or from a Reader interface. The following snippet, for example, constructs a data frame, prints it out, and then does a linear regression on the two values.

engine.eval("df <- data.frame(x=1:10, y=(1:10)+rnorm(n=10))");
engine.eval("print(lm(y ~ x, df))");

You should get output similar to the following:

   x      y
 1  1     -0.188
 2  2      3.144
 3  3      1.625
 4  4      3.426
 5  5       6.45
 6  6       5.85
 7  7      7.774
 8  8      8.495
 9  9      9.276
10 10     10.603

lm(formula = y ~ x, data = df)

(Intercept) x
-0.582       1.132


The ScriptEngine won’t print everything to standard out like the interactive REPL does, so if you want to output something, you’ll need to call the R print() command explicitly.

You can also collect the R commands in a separate file

# script.R
df <- data.frame(x=1:10, y=(1:10)+rnorm(n=10))
print(lm(y ~ x, df))

and evaluate the script using the following snippet:

engine.eval(new java.io.FileReader("script.R"));