com.pervasive.datarush.analytics.text

Class CalculateNGramFrequency

java.lang.Object

com.pervasive.datarush.operators.AbstractLogicalOperator

com.pervasive.datarush.operators.StreamingOperator

com.pervasive.datarush.operators.ExecutableOperator

com.pervasive.datarush.analytics.text.CalculateNGramFrequency

All Implemented Interfaces:

LogicalOperator, PipelineOperator<RecordPort>, RecordPipelineOperator

public class CalculateNGramFrequency
extends ExecutableOperator
implements RecordPipelineOperator

Calculates the n-gram frequencies for a tokenized text field. This operator can be used to determine the frequencies of each n-gram in the original text. The CalculateNGramFrequency operator has three properties: input field, output field, and the n to use. By default will calculate frequencies for an n of 2. The operator will output an NGramMap object that contains the n-grams and their associated frequencies. This object can then be used by other operators such as TextFrequencyFilter or ExpandTextFrequency that operate on a frequency model.

Constructor Summary

Constructors

Constructor and Description
CalculateNGramFrequency() Default constructor.
CalculateNGramFrequency(String textField) Constructor specifying the tokenized text field to determine the n-gram frequencies for.
CalculateNGramFrequency(String textField, int n) Constructor specifying the tokenized text field to determine the n-gram frequencies for and the n to use.

Method Summary

Modifier and Type	Method and Description
protected void	computeMetadata(StreamingMetadataContext ctx) Implementations must adhere to the following contracts
protected void	execute(ExecutionContext ctx) Executes the operator.
RecordPort	getInput() Get the input port of this operator.
String	getInputField() Get the field to calculate the n-gram frequencies for.
int	getN() Get the N for the n-grams.
String	getNgramFreqOutputField() Get the field that will contain the n-gram frequncy map.
RecordPort	getOutput() Get the output port of this operator.
void	setInputField(String textField) Set the field to calculate the n-gram frequencies for.
void	setN(int n) Set the N for the n-grams.
void	setNgramFreqOutputField(String ngramFreqOutputField) Set the field that will contain the n-gram frequency map.

Methods inherited from class com.pervasive.datarush.operators.ExecutableOperator

cloneForExecution, getNumInputCopies, getPortSettings, handleInactiveOutput

Methods inherited from class com.pervasive.datarush.operators.AbstractLogicalOperator

disableParallelism, getInputPorts, getOutputPorts, newInput, newInput, newOutput, newRecordInput, newRecordInput, newRecordOutput, notifyError

Methods inherited from class java.lang.Object

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

Methods inherited from interface com.pervasive.datarush.operators.LogicalOperator

disableParallelism, getInputPorts, getOutputPorts

Constructor Detail

CalculateNGramFrequency

public CalculateNGramFrequency()

Default constructor. Use setInputField(String), #setNGramFreqOutputField(String) to set the name of the text field to count and the output field.

CalculateNGramFrequency

public CalculateNGramFrequency(String textField)

Constructor specifying the tokenized text field to determine the n-gram frequencies for.

Parameters:

textField - name of the tokenized text field in the input

CalculateNGramFrequency

public CalculateNGramFrequency(String textField,
                               int n)

Constructor specifying the tokenized text field to determine the n-gram frequencies for and the n to use.

Parameters:

textField - name of the tokenized text field in the input

n - the number of words per n-gram

Method Detail

setInputField

public void setInputField(String textField)

Set the field to calculate the n-gram frequencies for.

If this field does not exist in the input, or is not of type TokenizedText, an exception will be thrown at composition time.

Parameters:

textField - name of the tokenized text field in the input

getInputField

public String getInputField()

Get the field to calculate the n-gram frequencies for.

Returns:

name of the tokenized text field in the input

setNgramFreqOutputField

public void setNgramFreqOutputField(String ngramFreqOutputField)

Set the field that will contain the n-gram frequency map.

Parameters:

ngramFreqOutputField - name of the n-gram field in the output

getNgramFreqOutputField

public String getNgramFreqOutputField()

Get the field that will contain the n-gram frequncy map.

Returns:

name of the n-gram field in the output

setN

public void setN(int n)

Set the N for the n-grams. Defaults to 2.

Parameters:

n - the number of words per n-gram

getN

public int getN()

Get the N for the n-grams.

Returns:

the number of words per n-gram

getInput

public RecordPort getInput()

Get the input port of this operator.

Specified by:

getInput in interface PipelineOperator<RecordPort>

Returns:

input port

getOutput

public RecordPort getOutput()

Get the output port of this operator.

Specified by:

getOutput in interface PipelineOperator<RecordPort>

Returns:

output port

computeMetadata

protected void computeMetadata(StreamingMetadataContext ctx)

Description copied from class: StreamingOperator

Implementations must adhere to the following contracts

General

Regardless of input ports/output port types, all implementations must do the following:

1. Validation. Validation of configuration should always be performed first.
2. Declare parallelizability.. Implementations must declare parallelizability by calling StreamingMetadataContext.parallelize(ParallelismStrategy).

Input record ports

Implementations with input record ports must declare the following:

1. Required data ordering:
Implementations that have data ordering requirements must declare them by calling RecordPort#setRequiredDataOrdering, otherwise data may arrive in any order.
2. Required data distribution (only applies to parallelizable operators):
Implementations that have data distribution requirements must declare them by calling RecordPort#setRequiredDataDistribution, otherwise data will arrive in an unspecified partial distribution.

Note that if the upstream operator's output distribution/ordering is compatible with those required, we avoid a re-sort/re-distribution which is generally a very large savings from a performance standpoint. In addition, some operators may chose to query the upstream output distribution/ordering by calling RecordPort#getSourceDataDistribution and RecordPort#getSourceDataOrdering. These should be viewed as a hints to help chose a more efficient algorithm. In such cases, though, operators must still declare data ordering and data distribution requirements; otherwise there is no guarantee that data will arrive sorted/distributed as required.

Output record ports

Implementations with output record ports must declare the following:

1. Type: Implementations must declare their output type by calling RecordPort#setType.

Implementations with output record ports may declare the following:

1. Output data ordering: Implementations that can make guarantees as to their output ordering may do so by calling RecordPort#setOutputDataOrdering
2. Output data distribution (only applies to parallelizable operators): Implementations that can make guarantees as to their output distribution may do so by calling RecordPort#setOutputDataDistribution

Note that both of these properties are optional; if unspecified, performance may suffer since the framework may unnecessarily re-sort/re-distributed the data.

Input model ports

In general, there is nothing special to declare for input model ports. Models are implicitly duplicated to all partitions when going from non-parallel to parallel operators. The case of a model going from a parallel to a non-parallel node is a special case of a "model reducer" operator. In the case of a model reducer, the downstream operator, must declare the following:

1. Merge handler: Model reducers must declare a merge handler by calling AbstractModelPort#setMergeHandler.

Note that MergeModel is a convenient, re-usable model reducer, parameterized with a merge-handler.

Output model ports

SimpleModelPort's have no associated metadata and therefore there is never any output metadata to declare. PMMLPort's, on the other hand, do have associated metadata. For all PMMLPorts, implementations must declare the following:

1. pmmlModelSpec: Implementations must declare the PMML model spec by calling PMMLPort.setPMMLModelSpec.

Specified by:

computeMetadata in class StreamingOperator

Parameters:

ctx - the context

execute

protected void execute(ExecutionContext ctx)

Description copied from class: ExecutableOperator

Executes the operator. Implementations should adhere to the following contracts:

1. Following execution, all input ports must be at end-of-data.
2. Following execution, all output ports must be at end-of-data.

Specified by:

execute in class ExecutableOperator

Parameters:

ctx - context in which to lookup physical ports bound to logical ports