From morkus at protonmail.com  Wed Oct 25 12:50:41 2017
From: morkus at protonmail.com (Morkus)
Date: Wed, 25 Oct 2017 06:50:41 -0400
Subject: [Rd] How to create a table structure in Java code?
Message-ID: <TNxOU9bI1Nh3erxhoQT01mOAwutGoyscR-w7sumoj2hZY0fkKbVCK1Vl-Fwd_Vs-2NQjDQyRLNixrYz-8HA6X-tZZ-ltlk0mpWWp4QD6Q90=@protonmail.com>

Hi all,

Using RConsole, it's easy to get data from the database that you can use in an R Command. Like this:

(Reference case)

irisQuery <- dbGetQuery(conn, "select * from iris")
boxM(irisQuery [,-5], irisQuery[,5])

----

(Actual case this posting is about)

Yet, if I'm getting that same (sample IRIS) data, say, in a web service possibly POSTED from a SQL command, that same data might look like this (portion of the included iris data set below). I'm thus not sure how to package the data so R likes it.

Example R-included IRIS data from SQL output:

5.1,3.5,1.4,0.2,setosa,
4.9,3,1.4,0.2,setosa,
4.7,3.2,1.3,0.2,setosa,
4.6,3.1,1.5,0.2,setosa,
5,3.6,1.4,0.2,setosa,

I've tried various combinations in code to achieve what's simple in RConsole, but I can't get R to accept my structure.

- I've tried just including the data in a string.
- I've tried wrapping the data with "data"
- I've tried wrapping the data with "data.frame" (as below).

Here's my latest attempt:

String tableRead = "data.frame(5.1,3.5,1.4,0.2,setosa\n" +
"4.9,3,1.4,0.2,setosa\n" +
"4.7,3.2,1.3,0.2,setosa\n" +
"4.6,3.1,1.5,0.2,setosa\n" +
"5,3.6,1.4,0.2,setosa)" ;

// using parseAndEval below to give me actual error R is sending...
REXP rResponseObject = rConnection.parseAndEval("try(eval("+tableRead+"),silent=TRUE)");
if (rResponseObject.inherits("try-error"))
{
     System.out.println("R Serve Eval Exception : "+rResponseObject.asString());
}
REXP boxMResult = rConnection.eval("boxM("+ tableRead+ "[,-5]," + tableRead + "[, 5])");  // FAILS <<

----

Error in the above case is:

Disconnected from the target VM, address: '127.0.0.1:51356', transport: 'socket'
org.rosuda.REngine.REngineException: eval failed, request status: R parser: syntax error
at org.rosuda.REngine.Rserve.RConnection.parseAndEval(RConnection.java:454)
at org.rosuda.REngine.REngine.parseAndEval(REngine.java:108)
at net.example.start_r_fromjava.RStatisticsExample.main(RStatisticsExample.java:151)

Does the POSTed data need to be in a different format or am I just not framing it correctly?

Would appreciate any tips on how to package table data that might come from a SQL Query passed to Java code.

Thanks very much in advance,

- M

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[Rd] How to create a table structure in Java code?
Morkus