Hi Yong The way GenericUDF works is as follows.
*ObjectInspector initialize(ObjectInspector[] arguments) *is called only once for one GenericUDF instance used in your Hive query. This phase is for preparation steps of UDF, such as syntax check and type inference. *Object evaluate(DeferredObject[] arguments)* is called to evaluate against actual arguments. This should be where the actual calculation happens and where you can get the real values you talked about. Thanks, Chen On Wed, Sep 26, 2012 at 4:17 AM, java8964 java8964 <java8...@hotmail.com>wrote: > Hi, I am using Cloudera release cdh3u3, which has the hive 0.71 version. > > I am trying to write a hive UDF function as to calculate the moving sum. > Right now, I am having trouble to get the constrant value passed in in the > initialization stage. > > For example, let's assume the function is like the following format: > > msum(salary, 10) --------- salary is a int type column > > which means the end user wants to calculate the last 10 rows of salary. > > I kind of know how to implement this UDF. But I have one problem right now. > > 1) This is not a UDAF, as each row will return one data back as the moving > sum. > 2) I create an UDF class extends from the GenericUDF. > 3) I can get the column type from the ObjectInspector[] passed to me in > the initialize() method to verify that 'salary' and 10 both needs to be > numeric type (later one needs to be integer) > 4) But I also want to get the real value of 10, in this case, in the > initialize() stage, so I can create the corresponding data structure based > on the value end user specified here. > 5) I looks around the javadoc of ObjectInspector class. I know at run time > the real class of the 2nd parameter is WritableIntObjectInspector. I can > get the type, but how I can get the real value of it? > 6) This is kind of ConstantsObjectInspector, should be able to give the > value to me, as it already knows the type is int. What how? > 7) I don't want to try to get the value at the evaluate stage. Can I get > this value at the initialize stage? > > Thanks > > Yong > -- Chen Song
