org.apache.hadoop.hive.ql.udf.generic

Class GenericUDAFCorrelation

java.lang.Object

org.apache.hadoop.hive.ql.udf.generic.AbstractGenericUDAFResolver

org.apache.hadoop.hive.ql.udf.generic.GenericUDAFCorrelation

All Implemented Interfaces:

GenericUDAFResolver, GenericUDAFResolver2

public class GenericUDAFCorrelation
extends AbstractGenericUDAFResolver

Compute the Pearson correlation coefficient corr(x, y), using the following stable one-pass method, based on: "Formulas for Robust, One-Pass Parallel Computation of Covariances and Arbitrary-Order Statistical Moments", Philippe Pebay, Sandia Labs and "The Art of Computer Programming, volume 2: Seminumerical Algorithms", Donald Knuth. Incremental: n : mx_n = mx_(n-1) + [x_n - mx_(n-1)]/n : my_n = my_(n-1) + [y_n - my_(n-1)]/n : c_n = c_(n-1) + (x_n - mx_(n-1))*(y_n - my_n) : vx_n = vx_(n-1) + (x_n - mx_n)(x_n - mx_(n-1)): vy_n = vy_(n-1) + (y_n - my_n)(y_n - my_(n-1)): Merge: c_(A,B) = c_A + c_B + (mx_A - mx_B)*(my_A - my_B)*n_A*n_B/(n_A+n_B) vx_(A,B) = vx_A + vx_B + (mx_A - mx_B)*(mx_A - mx_B)*n_A*n_B/(n_A+n_B) vy_(A,B) = vy_A + vy_B + (my_A - my_B)*(my_A - my_B)*n_A*n_B/(n_A+n_B)

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	GenericUDAFCorrelation.GenericUDAFCorrelationEvaluator Evaluate the Pearson correlation coefficient using a stable one-pass algorithm, based on work by Philippe Pébay and Donald Knuth.

Constructor Summary

Constructors

Constructor and Description
GenericUDAFCorrelation()

Method Summary

Modifier and Type	Method and Description
GenericUDAFEvaluator	getEvaluator(TypeInfo[] parameters) Get the evaluator for the parameter types.

Methods inherited from class org.apache.hadoop.hive.ql.udf.generic.AbstractGenericUDAFResolver

getEvaluator

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

GenericUDAFCorrelation

public GenericUDAFCorrelation()

Method Detail

getEvaluator

public GenericUDAFEvaluator getEvaluator(TypeInfo[] parameters)
                                  throws SemanticException

Description copied from interface: GenericUDAFResolver

Get the evaluator for the parameter types. The reason that this function returns an object instead of a class is because it is possible that the object needs some configuration (that can be serialized). In that case the class of the object has to implement the Serializable interface. At execution time, we will deserialize the object from the plan and use it to evaluate the aggregations.

If the class of the object does not implement Serializable, then we will create a new instance of the class at execution time.

Specified by:

getEvaluator in interface GenericUDAFResolver

Overrides:

getEvaluator in class AbstractGenericUDAFResolver

Parameters:

parameters - The types of the parameters. We need the type information to know which evaluator class to use.

Throws:

SemanticException