This blog post looks at how to format the output or the returned returns from an Oracle R Enterprise (ORE), user defined R function, that is run using a SELECT statement in SQL.
Sometimes this can be a bit of a challenge to work out, but it can be relatively easy once you have figured out how to do it. The following examples works through some scenarios of different results sets from a user defined R function that is stored in the Oracle Database.
To run that user defined R function using a SELECT statement I can use one of the following ORE SQL functions.
- rqEval
- rqTableEval
- "rqGroupEval"
- rqRowEval
For simplicity we will just use the first of these ORE SQL functions to illustrate the problem and how to go about solving it. The rqEval ORE SQL function is a generate purpose function to call a user defined R script stored in the database. The function does not require any input data set and but it will return some data. You could use this to generate some dummy/test data or to find some information in the database. Here is noddy example that returns my name.
BEGIN
--sys.rqScriptDrop('GET_NAME');
sys.rqScriptCreate('GET_NAME',
'function() {
res<-data.frame("Brendan")
res
} ');
END;
To call this user defined R function I can use the following SQL.
select *
from table(rqEval(null,
'select cast(''a'' as varchar2(50)) from dual',
'GET_NAME') );
For text strings returned you need to cast the returned value giving a size.
If we have a numeric value being returned we can don't have to use the cast and instead use '1' as shown in the following example. This second example extends our user defined R function to return my name and a number.
BEGIN
sys.rqScriptDrop('GET_NAME');
sys.rqScriptCreate('GET_NAME',
'function() {
res<-data.frame(NAME="Brendan", YEAR=2017)
res
} ');
END;
To call the updated GET_NAME function we now have to process two returned columns. The first is the character string and the second is a numeric.
select *
from table(rqEval(null,
'select cast(''a'' as varchar2(50)) as "NAME", 1 AS YEAR from dual',
'GET_NAME') );
These example illustrate how you can process character strings and numerics being returned by the user defined R script.
The key to setting up the format of the returned values is knowing the structure of the data frame being returned by the user defined R script. Once you know that the rest is (in theory) easy.
