Using org.rosuda.JRI.REXP objects with R values

Question

Hi,
As JRI and rJava use JNI, I thought I'd try postin this here...
I'm a bit confused about how REXP and Rengine in org.rosuda.JRI works.
If I use the example code....
public REXP getDistance (Rengine re)
         //...open a file and assign some data to 'data'.....then...      
        REXP rexp = re.eval ("dist_out <- data.matrix(data, rownames.force = NA)");
        return rexp;
    }... then the following code knows what 'dist_out' is, that it's of class 'matrix' and works fine...
public Rengine getNJTree (REXP rexp, Rengine re)
        re.eval ("library (ape)");
        re.eval ("tree_mr <- nj(dist_out)");
        re.eval ("plot(tree_mr)");
        System.out.println ("Exiting getNJTree");
        return re;
    }But, if I use....
public Rengine getNJTree (REXP rexp, Rengine re)
        re.eval ("library (ape)");
        re.eval ("tree_mr <- nj("+rexp+")");
        re.eval ("plot(tree_mr)");
       return re;
    }...then I get an error - "object tree_mr not found"
and this is because rexp is not being recognised as the 'dist_out' which was assigned to it earlier.
If I run the code rexp.getContent(), I get the content as "[D@129b0e1", which I guess is some reference?
Even if I try....
{code} public Rengine getNJTree (REXP rexp, Rengine re)
double[][] matrix = rexp.asDoubleMatrix ();
re.eval ("library (ape)");
re.eval ("tree_mr <- nj("+matrix+")");
re.eval ("plot(tree_mr)");
return re;
}{code}
....I still get "object tree_mr not found"
So, I'm obviously doing something wrong here, but I can't figure out for the life of me what it is.
Any help or explaination would be very welcome.
Many thanks!

Answer 1

As JRI and rJava use JNI, I thought I'd try postin this here...I cannot image why. The issue has nothing whatsoever to do with JNI.
Locking this thread.