使用Java的R arules软件包中的问题

Question

For a university project I have to implement arules(package of R) in java. I have successfully integrated R and java using JRI. I did not understand how to get output of " inspect(Groceries[1:1]) ". I have tried with asString(),asString[]() but this gives me following error:

Exception in thread "main" java.lang.NullPointerException
at TestR.main(TestR.java:11)

Also, how can implement summary(Groceries) in java? How to get output of summary in String array or string?

R code:

>data(Groceries)
>inspect(Groceries[1:1])
>summary(Groceries)

Java code:

import org.rosuda.JRI.Rengine;
import org.rosuda.JRI.REXP;

public class TestR {
    public static void main(String[] args){
    Rengine re = new Rengine(new String[]{"--no-save"}, false, null);

    re.eval("library(arules)");
    re.eval("data(Groceries)");
    REXP result = re.eval("inspect(Groceries[1:1])");

    System.out.println(result.asString());
    }

}

Answer 1

Appears that the inspect function in pkg:arules returns NULL. The output you see is a "side-effect". You can attempt to "capture output" but this is untested since I don't have experience with this integration across languages. Try instead.:

REXP result = re.eval("capture.output( inspect(Groceries[1:1]) )");

In an R console session you will get:

library(arules)
data("Adult")
rules <- apriori(Adult)
val <- inspect(rules[1000])

> str(val)
 NULL
> val.co <- capture.output(inspect(rules[1000]))
> val.co
[1] "  lhs                         rhs                              support confidence     lift"
[2] "1 {education=Some-college,                                                                "
[3] "   sex=Male,                                                                              "
[4] "   capital-loss=None}      => {native-country=United-States} 0.1208181  0.9256471 1.031449"

But I haven't tested this in a non-interactive session. May need to muck with the file argument to capture.output , ... or it may not work at all.