Calling sqldf package of R in Java using JRI

Question

I have developed java code using JRI for executing the R code on Java. Now, I have come across a problem (picking up distinct values in the column of a data frame) where I have to use sqldf package of R and am trying to use its function in my Java code. Here is the sample code (Orange is the dataset already present in R by default):

public class RCode2 {
    public static JRIEngine re;
    private static  org.rosuda.REngine.REXP rexp;

    public RCode2()
    {
        try {
            re = new JRIEngine(new String [] {"--vanilla"});
        } catch (REngineException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
        }
        System.out.println("Rengine created, waiting for R");               
    }
    public static void main(String[] args) {
        RCode2 rCode2= new RCode2();
        rCode2.testSqldf(); 
        re.close();
    }
    public void testSqldf(){
        rexp=re.parseAndEval("library(sqldf,lib.loc=\"C:/Program Files/R/R-"+"2.15.0/library\")\n");
        System.out.println(rexp.isNull());
        rexp=re.parseAndEval("dframe<-sqldf(\"select * from Orange\")");
        System.out.println(rexp.isNull());
    }
}

The output of the above code is:

Rengine created, waiting for R
true
true

This means that "dframe" contains nothing. But when I try to run the same sqldf func: sqldf("select * from Orange") on R then it gives me 35 rows. How do I make use of sqldf functions in java so as to get desired results?

My environment variables are set as follows:

R_HOME=C:\Program Files\R\R-2.15.0
R_LIBS=C:\Program Files\R\R-2.15.0\library
R_LIBS_USER=C:\Program Files\R\R-2.15.0\library
Path=C:\Program Files\R\R-2.15.0\bin\i386;C:\Program Files\R\R-2.15.0\library\rJava\jri

Answer 1

The code you posted doesn't even compile. After cleaning it up it works just fine:

C:\Program Files\R\R-2.15\library\rJava\jri>run RCode2
Rengine created, waiting for R
org.rosuda.REngine.REXPString@10d448[14]
org.rosuda.REngine.REXPGenericVector@1bf216a+[3]named

If you have issues with your code you should make sure you provide I/O from R console so you can actually see errors caused by your code (see TextCondole class in the examples).

Finally, stats-rosuda-devel mailing list is the place to ask about rJava/JRI.

The code:

import org.rosuda.REngine.JRI.*;
import org.rosuda.REngine.*;

public class RCode2 {
    public static JRIEngine re;
    private static  org.rosuda.REngine.REXP rexp;

    public RCode2()
    {
        try {
            re = new JRIEngine(new String [] {"--vanilla"});
        } catch (REngineException e) {
            e.printStackTrace();
        }
        System.out.println("Rengine created, waiting for R");               
    }
    public static void main(String[] args) {
        RCode2 rCode2= new RCode2();
        rCode2.testSqldf(); 
        re.close();
    }
    public void testSqldf(){
        try {
            rexp = re.parseAndEval("library(sqldf)");
            System.out.println(rexp);
            rexp = re.parseAndEval("dframe<-sqldf(\"select * from Orange\")");
            System.out.println(rexp);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}