Hi,
Many of the pig (and hadoop) classes use java generic type definition.
The method signature for exec is:
abstract public T exec(Tuple input) throws IOException;
So if your method is returning InternalMap you need to define your eval
function class as such:
public class MyEvalFunc<InternalMap>{
@Override
public InternalMap exec(Tuple input) throws IOException{
DataBag bag = (DataBag) input.get(0);
}
@Override
public Schema outputSchema(Schema input) {
return new Schema(new Schema.FieldSchema(null, DataType.BAG));
}
}
@Override is a great way of letting your IDE now that you think this method
is overriding something. If it complains with an error it means you've
missed out something in the method signature that is not 100%.
The argument to the function must be a Tuple.
The tuple is populated with the arguments passed to your udf.
So that if you have in the pig script MyUDF('a','b','c')
The input Tuple will contain values
(String)input.get(0) == 'a'
(String)input.get(1) == 'b'
(String)input.get(2) == 'c'
In your case the input.get(0) will contain a type DataBag.
Cheers,
Gerrit
-----Original Message-----
From: Kris Coward [mailto:[email protected]]
Sent: Friday, November 26, 2010 6:27 PM
To: [email protected]
Subject: Difficulty extending EvalFunc
Hi,
I'm trying to write a UDF to take a bag of http get arguments (e.g.
{(s=556477989), (ts=1265964662)} ) and turn them into a map (e.g.
[s#556477989, ts#1265964662] ), and have written a class extending
EvalFunc, but am having no end of trouble declaring/defining the exec
method. My first shot at compiling it had code like this:
public InternalMap exec(DataBag input) throws IOException {
and produced the compile-time error:
httpArgParse.java:11: myudfs.httpArgParse is not abstract and does not
override abstract method exec(org.apache.pig.data.DataBag)
clumsily trying at sticking an @Override before it (as I noticed was
done in TOKENIZE), instead produced:
httpArgParse.java:12: method does not override or implement a method
from a supertype
I have a hunch that this isn't too awful a problem for someone who's
done much Java coding in the past decade, but I've been away from the
language for about 12 years now, and it seems to have changed
significantly in that time.
Cheers,
Kris
--
Kris Coward http://unripe.melon.org/
GPG Fingerprint: 2BF3 957D 310A FEEC 4733 830E 21A4 05C7 1FEB 12B3
