[Rd] Fetching Warning Messages

[Nikhil Shah]

Hi,

    I am facing one problem of fetching R warning messages in Java Code
using Rserve. It is easier to trap R Error messages by using catching
RSrvException. I came to know one way of fetching R Warning messages, i.e.
using "withCallingHandlers", below is my Java Program, which uses
withCallingHandlers of R :
import org.rosuda.JRclient.*;

---------------------------RWarning.java-----------------------
class RWarning
{
   public static void main(String args[])
  {
     try
     {
       String hostName = null;
       hostName = args[0];
       Rconnection c = new Rconnection(hostName);
       c.voidEval("lastWarning <- NULL");
       c.voidEval("withCallingHandlers(
{x<-sqrt(-9);y<-matrix(1:9,ncol=4);z<-sqrt(4)} , warning = function (w) {
lastWarning <<- paste(lastWarning,as.character(w))})"); //This will generate
warning message[sqrt(-9)], another warning message [ matrix(1:9,ncol=4) ]
and successful completion [ sqrt(4) ]
        System.out.println(c.eval("z").asDouble());
        System.out.println(c.eval("lastWarning").asString());
        c.close();
        System.out.println("DONE");
      }
      catch(RSrvException  e)
      {
         System.out.println("Error : " + e.getMessage());
         e.printStackTrace();
      }
   }
}
---------------------------End Of RWarning.java-----------------------

Output of above program is (as expected) :

2.0
simpleWarning in sqrt(-9): NaNs produced
simpleWarning: data length [9] is not a sub-multiple or multiple of the
number of columns [4] in matrix

DONE



     Now my query is that if there is any way of using warnings() function
in Java Program to fetch all warnings. I used it in my program but returns
me NULL instead of warning messages. I also used last.warning but it Java
Program gives an error saying that last.warning object is not found. I have
pasted both the java code below :

This is the java program that I have written to use "last.warning" object of
R. Please explain me where the error could be.

------------Code of RWarning1.java----------------

import org.rosuda.JRclient.*;

class RWarning1
{
  public static void main(String args[])
  {
    try
    {
      String hostName = null;
      hostName = args[0];
      Rconnection c = new Rconnection(hostName);
      System.out.println(c.eval("x<-sqrt(-9)").asString());
      System.out.println(c.eval("last.warning").asString());
      c.close();
      System.out.println("DONE");
    }
    catch(RSrvException  e)
    {
      System.out.println("Error : " + e.getMessage());
      e.printStackTrace();
    }
  }
}
------------End of code of RWarning1.java------------------

output of RWarning1.class

null
Error : Request return code: 127 [request status: Error (127)]
org.rosuda.JRclient.RSrvException: Request return code: 127 [request status:
Err
or (127)]
        at org.rosuda.JRclient.Rconnection.eval(Rconnection.java:190)
        at RWarning.main(RWarning.java:13)

In other words, when I use "last.warning" in eval method, I simply get an
exception, instead of value of last.warning.


Below is the java code of using warnings() function.

------------Code of RWarning2.java----------------

import org.rosuda.JRclient.*;

class RWarning2
{
  public static void main(String args[])
  {
  try
  {
    String hostName = null;
    hostName = args[0];
    Rconnection c = new Rconnection(hostName);
    System.out.println(c.eval("x<-sqrt(-9)").asString());

System.out.println(c.eval("paste(capture.output(warnings()),collapse='\n')")
.asString());
    c.close();
    System.out.println("DONE");
  }
  catch(RSrvException  e)
  {
    System.out.println("Error : " + e.getMessage());
    e.printStackTrace();
  }
}
}
------------End of code of RWarning2.java------------------
output of RWarning2.class

null
NULL
DONE


  Please let me know where I am making mistake.

Regards,

Nikhil Shah