Introduction

This page describes how to install the eclipse plugin that helps calling R from Java using JRI. It is possible to transfer data between R and Java. In this tutorial we look at the objects in java that hold data returned from R.

RBool

RBool holds the boolean value. R boolean can take three states – true, false and NA. RBool has three methods isNA(), isTRUE() and isFALSE(). Here’s an example that shows how to get the return value from R into RBool

        RBool booleanValue = re.eval("1==1").asBool();
		System.out.println(booleanValue.toString());

		booleanValue = re.eval("1==2").asBool();
		System.out.println(booleanValue.toString());

RFactor

RFactor stores the R factor variables. factors in R are used to store categorical values. Here’s an example of factors in R

> days=c('Monday','Tuesday','Wednesday','Thursday','Friday','Monday','Tuesday');
> factor(days)
[1] Monday    Tuesday   Wednesday Thursday  Friday    Monday    Tuesday  
Levels: Friday Monday Thursday Tuesday Wednesday

This is how we do it from java

RFactor factors =
re.eval("factor(c('Monday','Tuesday','Wednesday','Thursday','Friday','Monday','Tuesday'))")
.asFactor();
System.out.println(factors.toString());

//Output:
//{levels=("Friday","Monday","Thursday","Tuesday","Wednesday"),ids=(1,3,4,2,0,1,3)}

RList

RList is of type entry=value. The entry is stored in “head” and the value is stored in “body”. It is possible to retrieve body for a particular head using the method at(String).

RList list = re
			.eval("list(name=\"studytrails\",website=\"www.studytrails.com\",number=3)")
			.asList();
list.
String[] keys = list.keys();
for (String key : keys) {
	System.out.println("key->" + key + "::value->" + list.at(key));
}
//output
//key->name::value->[STRING "studytrails"]
//key->website::value->[STRING "www.studytrails.com"]
//key->number::value->[REAL* (3.0)]

To get the value’s string or number, use the asInt(), asString() or asDouble() method on the value object. The type can be obtained using the getType() method.

RVector

RVector represents the named generic vectors in R. It has all methods that java.util.Vector has plus methods at() and at(String)

RVector vector = (re.eval("data.frame(c(1:3),c(2:4))").asVector());
System.out.println(vector);
System.out.println(vector.at(0));

REXP

If none of the above solves your problem, then look at REXP. This encapsulates all R objects. RList, RVector, RBool and RFactor have all been converted from REXP, however, if you need final control then this is your class.