Call R from JAVA to get Chi-squared statistic and p-value

Question

I have two 4*4 matrices in JAVA, where one matrix holds observed counts and the other expected counts.

I need an automated way to calculate the p-value from the chi

Answer 1

Rserve is another way to get your data from Java to R and back. It is a server which takes R scripts as string inputs. You can use some string parsing and conversion in Java to convert the matrices into strings that can be input into R.

import org.rosuda.REngine.REXP;
import org.rosuda.REngine.Rserve.RConnection;


public class RtestScript {

private String emailTestScript = "open <- c('O', 'O', 'N', 'N', 'O', 'O', 'N', 'N', 'N', 'O', " +
        " 'O', 'N', 'N', 'O', 'O', 'N', 'N', 'N', 'O');" +
        "testgroup <- c('A', 'A', 'A','A','A','A','A','A','A','A', 'B'," +
        "'B', 'B', 'B', 'B', 'B', 'B', 'B', 'B');" +
        "emailTest <- data.frame(open, testgroup);" +
        "emailTable<- table(emailTest$open, emailTest$testgroup);" +
        "emailResults<- prop.test(emailTable, correct=FALSE);" +
        "print(emailResults$p.value);";

public void executeRscript() {
    try {
        //Make sure to type in library(Rserve); Rserve() in Rstudio before running this
        RConnection testConnection = new RConnection();

        REXP testExpression = testConnection.eval(emailTestScript);
        System.out.println("P value: " + testExpression.asString());
    } catch(Exception e) {
        e.printStackTrace();
    }
}
}

Here is some more information on Rserve. Incidentally, this is also how Tableau can communicate with R as well with their R connection.

https://cran.r-project.org/web/packages/Rserve/index.html