org.apache.pig.builtin

Class DoubleRoundTo

java.lang.Object

org.apache.pig.EvalFunc<java.lang.Double>

org.apache.pig.builtin.DoubleRoundTo

public class DoubleRoundTo
extends EvalFunc<java.lang.Double>

ROUND_TO safely rounds a number to a given precision by using an intermediate BigDecimal. The too-often seen trick of doing (1000.0 * ROUND(x/1000)) is not only hard to read but also fails to produce numerically accurate results. Given a single data atom and number of digits, it returns a double extending to the given number of decimal places. The result is a multiple of ten to the power given by the digits argument: a negative value zeros out correspondingly many places to the left of the decimal point: ROUND_TO(0.9876543, 3) is 0.988; ROUND_TO(0.9876543, 0) is 1.0; and ROUND_TO(1234.56, -2) is 1200.0. The optional mode argument specifies the rounding mode; by default, 'HALF_EVEN' is used.

Nested Class Summary

Nested classes/interfaces inherited from class org.apache.pig.EvalFunc

EvalFunc.SchemaType

Field Summary

Fields inherited from class org.apache.pig.EvalFunc

log, pigLogger, reporter, returnType

Constructor Summary

Constructors

Constructor and Description
DoubleRoundTo()

Method Summary

Methods

Modifier and Type	Method and Description
boolean	allowCompileTimeCalculation() Whether the UDF should be evaluated at compile time if all inputs are constant.
java.lang.Double	exec(Tuple input) java level API
java.util.List<FuncSpec>	getArgToFuncMapping() Allow a UDF to specify type specific implementations of itself.

Methods inherited from class org.apache.pig.EvalFunc

finish, getCacheFiles, getInputSchema, getLogger, getPigLogger, getReporter, getReturnType, getSchemaName, getSchemaType, getShipFiles, isAsynchronous, outputSchema, progress, setInputSchema, setPigLogger, setReporter, setUDFContextSignature, warn

Methods inherited from class java.lang.Object

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

Constructor Detail

DoubleRoundTo

public DoubleRoundTo()

Method Detail

exec

public java.lang.Double exec(Tuple input)
                      throws java.io.IOException

java level API

Specified by:

exec in class EvalFunc<java.lang.Double>

Parameters:

input - expects a numeric value to round, a number of digits to keep, and an optional rounding mode.

Returns:

output returns a single numeric value, the number with only those digits retained

Throws:

java.io.IOException

getArgToFuncMapping

public java.util.List<FuncSpec> getArgToFuncMapping()
                                             throws FrontendException

Description copied from class: EvalFunc

Allow a UDF to specify type specific implementations of itself. For example, an implementation of arithmetic sum might have int and float implementations, since integer arithmetic performs much better than floating point arithmetic. Pig's typechecker will call this method and using the returned list plus the schema of the function's input data, decide which implementation of the UDF to use.

Overrides:

getArgToFuncMapping in class EvalFunc<java.lang.Double>

Returns:

A List containing FuncSpec objects representing the EvalFunc class which can handle the inputs corresponding to the schema in the objects. Each FuncSpec should be constructed with a schema that describes the input for that implementation. For example, the sum function above would return two elements in its list:

1. FuncSpec(this.getClass().getName(), new Schema(new Schema.FieldSchema(null, DataType.DOUBLE)))
2. FuncSpec(IntSum.getClass().getName(), new Schema(new Schema.FieldSchema(null, DataType.INTEGER)))

This would indicate that the main implementation is used for doubles, and the special implementation IntSum is used for ints.

Throws:

FrontendException

allowCompileTimeCalculation

public boolean allowCompileTimeCalculation()

Description copied from class: EvalFunc

Whether the UDF should be evaluated at compile time if all inputs are constant. This is applicable for most UDF, however, if a UDF will access hdfs file which is not available at compile time, it has to be false

Overrides:

allowCompileTimeCalculation in class EvalFunc<java.lang.Double>

Returns:

Whether or not compile time calculation is allowed, default to false to ensure legacy UDF will get the right behavior