If you have created a function in R, how do you call it in Java using Renjin?

java, r, renjin

Solution

When you run

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

the `script.R` file is parsed and the statements in the file are executed in the global environment. If your file only defines the function, then it will indeed not be called.

There are a few options to execute the function:

extend `script.R` to include a call to `bin`, e.g.

bin <- function(arg1, arg2, arg3) {
//some code here
}
bin(arg1 = 1, arg2 = 2, arg3 = 3)

evaluate `script.R`, construct and evaluate the command in the Java code, e.g.

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

followed by

engine.eval("bin(arg1 = " + 1 + ", arg2 = " + 2 + ", arg3 = " + 3 + ")");

evaluate `script.R`, create variables in the global environment, and execute the `bin` function:

engine.eval(new java.io.FileReader("script.R"));
engine.eval("arg1 <- 1; arg2 <- 2; arg3 <- 3");
engine.eval("bin(arg1, arg2, arg3)");

Each option gives you different levels of flexibility, therefore you can experiment to see which works best for you.

Problem

Let's say I have created a function in R like ``` bin <- function(arg1, arg2, arg3) { //some code here } ``` I am using Renjin to run R on the JVM. From my Java program, I want to call my R function `bin`. I know you need to use something similar to this first just to access R ``` ScriptEngineManager manager = new ScriptEngineManager(); // create a Renjin engine: ScriptEngine engine = manager.getEngineByName("Renjin"); ``` but once that is done, how exactly do I access my R function? This function is stored in a separate file. I know that to run an R script (let's call this `script.R`), you use ``` engine.eval(new java.io.FileReader("script.R")); ``` but that doesn't allow argument passing in functions in the file... it just runs the whole thing. Would I have to just rewrite the function using R/Renjin in my Java program? Or is there an efficient way to call the function? Thank you!

Original source