Get same output as R console in Java using JRI

Question

When I enter the following commands directly into the R console

library("xts")
mySeries <- xts(c(1.0, 2.0, 3.0, 5.0, 6.0), order.by=c(ISOdatetime(2001, 1, 1, 0, 0, 0), ISOdatetime(2001, 1, 2, 0, 0, 0), ISOdatetime(2001, 1, 3, 0, 0, 0), ISOdatetime(2001, 1, 4, 0, 0, 0), ISOdatetime(2001, 1, 5, 0, 0, 0)))
resultingSeries <- to.monthly(mySeries)
resultingSeries

I will get an output like this

             mySeries.Open mySeries.High mySeries.Low mySeries.Close
Jan 2001             1             6            1              6

When I look into the attributes, I see the following output

attributes(resultingSeries)

$dim
[1] 1 4

$dimnames
$dimnames[[1]]
NULL

$dimnames[[2]]
[1] "mySeries.Open"  "mySeries.High"  "mySeries.Low"   "mySeries.Close"
$index
[1] 978307200
attr(,"tclass")
[1] "yearmon"
$tclass
[1] "POSIXct" "POSIXt" 
$tzone
[1] ""
$class
[1] "xts" "zoo"
$.indexCLASS
[1] "yearmon"

This is the same I get in Java. I'm wondering where the magic happens so that I see the nice output I get in R. I have no access to the event loop, since I'm using JRI like this (since, it's the recommended way and simplifies error handling):

REngine engine = REngine.engineForClass("org.rosuda.REngine.JRI.JRIEngine");
REXP result = engine.parseAndEval(...)

/edit In Java I execute each command from above as follows:

REXP result = engine.parseAndEval("resultingSeries") // or any other command

What I get is

org.rosuda.REngine.REXPDouble@4ac66122+[12]

The payload being doubles: 1, 6, 1, 6 The attributes are the same as specified above.

Now R does some magic to display the output above. Is there a way I can get the same output without having to create it manually by myself? Where's the implementation stored, that R gets the above mentioned output?

So I don't understand, do you want to view the R output in the Java console? also could you post the Java Code (with JRI/R) so i can see the full problem? — Yehoshaphat Schellekens
– Yehoshaphat Schellekens, Commented Feb 4, 2015 at 9:02
I tried to improve my question. I can't really post exactly what I get in java, because it's a complex object. I hope this helps. Yes I want to get the output as string in Java or know, how R does it's formatting. — Daniel
– Daniel, Commented Feb 4, 2015 at 10:22
i meant where is the Java implementation of R? , it seems like you haven't activated any R code within Java, im looking for Java code like "engine.eval(" some r code.....") , is this all the code you used? — Yehoshaphat Schellekens
– Yehoshaphat Schellekens, Commented Feb 4, 2015 at 11:45
Yes that's all. I added the java snipets in my last edit. I execute engine.parseAndEval(commandString), commandString being the same commands I entered in R. Please note I use the parseAndEval function of REngine, which offers better error handling. — Daniel
– Daniel, Commented Feb 4, 2015 at 12:26

David Arenburg · Accepted Answer · 2015-02-04 12:57:06Z

2

Here is a piece of code that will work, here i extracted the first element of the field mySeries.Open from the object resultingSeries (which i converted to a data frame) which is equal to 1, notice that you can't pass all of the resultingSeries object strait into Java, you will need to break it down.

package stackoverflow;

import org.rosuda.JRI.REXP;
import org.rosuda.JRI.Rengine;
/**
 *
 * @author yschellekens
 */
public class StackOverflow {      
   public static void main(String[] args) throws Exception {
    String[] Rargs = {"--vanilla"};
    Rengine rengine = new Rengine(  Rargs, false, null);
    rengine.eval("library('xts')");
    rengine.eval("mySeries <- xts(c(1.0, 2.0, 3.0, 5.0, 6.0), order.by=c(ISOdatetime(2001, 1, 1, 0, 0, 0), ISOdatetime(2001, 1, 2, 0, 0, 0), ISOdatetime(2001, 1, 3, 0, 0, 0), ISOdatetime(2001, 1, 4, 0, 0, 0), ISOdatetime(2001, 1, 5, 0, 0, 0)))");
    rengine.eval("resultingSeries <- to.monthly(mySeries)");
    rengine.eval("resultingSeries<-as.data.frame(resultingSeries)");              
    REXP result= rengine.eval("resultingSeries$mySeries.Open");
    System.out.println("Greeting from R: "+result.asDouble());
   }
}

And the Java output:

run:
Greeting from R: 1.0

edited Feb 4, 2015 at 12:57

David Arenburg

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answered Feb 4, 2015 at 12:49

Yehoshaphat Schellekens

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1 Comment

Daniel Over a year ago

Thanks for your effort but this is not what I'm looking for. I know how to access simple values but I wanted to access the R console output which it somehow generates. I'm sorry that I couldn't explain myself better.

Daniel · Accepted Answer · 2015-02-04 16:16:43Z

2

I figured out the following workaround. The solution is far from perfect.

R offers a command to save its console output as characters vector.

capture.output( {command} )

We can access the output using

REXPString s = rengine.parseAndEval("capture.output( to.monthly(mySeries))")
String[] output = result.asStrings()

The variable output will contain all output lines

[0]             mySeries.Open mySeries.High mySeries.Low mySeries.Close
[1]Jan 2001             1             6            1              6

Alternatively you coud use JRIEngine and attack yourself to the event loop, which it did not want in my case (due to the more complicated error handling).

answered Feb 4, 2015 at 16:16

Daniel

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