org.apache.pig.builtin

Class SUBSTRING

java.lang.Object

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

org.apache.pig.builtin.SUBSTRING

Direct Known Subclasses:

SUBSTRING

public class SUBSTRING
extends EvalFunc<java.lang.String>

SUBSTRING implements eval function to get a part of a string. Example: A = load 'mydata' as (name); B = foreach A generate SUBSTRING(name, 10, 12); First argument is the string to take a substring of.
Second argument is the index of the first character of substring.
Third argument is the index of the last character of substring.
if the last argument is past the end of the string, substring of (beginIndex, length(str)) is returned.

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
SUBSTRING()

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.String	exec(Tuple input) Method invoked on every tuple during foreach evaluation
java.util.List<FuncSpec>	getArgToFuncMapping() Allow a UDF to specify type specific implementations of itself.
Schema	outputSchema(Schema input) Report the schema of the output of this UDF.

Methods inherited from class org.apache.pig.EvalFunc

finish, getCacheFiles, getInputSchema, getLogger, getPigLogger, getReporter, getReturnType, getSchemaName, getSchemaType, getShipFiles, isAsynchronous, 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

SUBSTRING

public SUBSTRING()

Method Detail

exec

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

Method invoked on every tuple during foreach evaluation

Specified by:

exec in class EvalFunc<java.lang.String>

Parameters:

input - tuple; first column is assumed to have the column to convert

Returns:

result, of type T.

Throws:

java.io.IOException

outputSchema

public Schema outputSchema(Schema input)

Description copied from class: EvalFunc

Report the schema of the output of this UDF. Pig will make use of this in error checking, optimization, and planning. The schema of input data to this UDF is provided.

The default implementation interprets the OutputSchema annotation, if one is present. Otherwise, it returns null (no known output schema).

Overrides:

outputSchema in class EvalFunc<java.lang.String>

Parameters:

input - Schema of the input

Returns:

Schema of the output

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.String>

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.String>

Returns:

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