org.datavec.api.transform.reduce

Interface ColumnReduction

All Superinterfaces:

ColumnOp, Serializable

public interface ColumnReduction
extends Serializable, ColumnOp

A column reduction defines how a single column should be reduced. Used in conjunction with Reducer to provide custom reduction functionality.

Author:

Alex Black

Method Summary

Modifier and Type	Method and Description
ColumnMetaData	getColumnOutputMetaData(String newColumnName, ColumnMetaData columnInputMeta) Post-reduce: what is the metadata (type, etc) for this column? For example: a "count unique" operation on a String (StringMetaData) column would return an Integer (IntegerMetaData) column
String	getColumnOutputName(String columnInputName) Post-reduce: what is the name of the column? For example, "myColumn" -> "mean(myColumn)"
Writable	reduceColumn(List<Writable> columnData) Reduce a single column.

Methods inherited from interface org.datavec.api.transform.ColumnOp

columnName, columnNames, getInputSchema, outputColumnName, outputColumnNames, setInputSchema, transform

Method Detail

reduceColumn

Writable reduceColumn(List<Writable> columnData)

Reduce a single column. Note: The List<Writable> here is a single column in a reduction window, and NOT the single row (as is usually the case for List<Writable> instances

Parameters:

columnData - The Writable objects for a column

Returns:

Writable containing the reduced data

getColumnOutputName

String getColumnOutputName(String columnInputName)

Post-reduce: what is the name of the column? For example, "myColumn" -> "mean(myColumn)"

Parameters:

columnInputName - Name of the column before reduction

Returns:

Name of the column after the reduction

getColumnOutputMetaData

ColumnMetaData getColumnOutputMetaData(String newColumnName,
                                       ColumnMetaData columnInputMeta)

Post-reduce: what is the metadata (type, etc) for this column? For example: a "count unique" operation on a String (StringMetaData) column would return an Integer (IntegerMetaData) column

Parameters:

columnInputMeta - Metadata for the column, before reduce

Returns:

Metadata for the column, after the reduction