[R] An example of using rJava

[Jason Liao]

I have received a few private emails asking for some simple
demonstration of calling Java code from R using the rJava package
(which can be installed directly inside R). Here is one example for
convolving two vectors (an example in the R manual about linking C with
R).

First write a Java program


public class my_convolve
{            	
     public static double[] convolve(double[] a, double[] b)
     {
         int n1 = a.length;
         int n2 = b.length;
         int n3 = n1+n1-1;
         
         double[] c = new double[n3];
         for(int i=0; i<n1; i++)
            for(int j=0; j<n2; j++) c[i+j] += a[i]*b[j];
            
         return c;
      }   
    }     
Compile the Java code.

now inside R

library(rJava) #load the rJava library
.jinit(classpath="c:/liao_all/importance_sampling/java",
parameters="-Xmx512m")
#the above is to load the Java virtual machine,
"c:/liao_all/importance_sampling/java" is where the java code is.

x = runif(1000)
y = runif(1000)
#the above are two vectors to convolve

#now you can call the Java method as
z=.jcall("my_convolve", "[D", "convolve", x,y)
#z stores the result

Hope this helps.





Jason Liao, http://www.geocities.com/jg_liao    
Associate Professor of Biostatistics
Drexel University School of Public Health
245 N. 15th Street, Mail Stop 660
Philadelphia, PA 19102-1192
phone 215-762-3934


 
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