public interface ColumnReduction extends java.io.Serializable, ColumnOp
Reducer
to provide custom reduction functionality.Modifier and Type | Method and Description |
---|---|
ColumnMetaData |
getColumnOutputMetaData(java.lang.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
|
java.lang.String |
getColumnOutputName(java.lang.String columnInputName)
Post-reduce: what is the name of the column?
For example, "myColumn" -> "mean(myColumn)"
|
Writable |
reduceColumn(java.util.List<Writable> columnData)
Reduce a single column.
|
columnName, columnNames, getInputSchema, outputColumnName, outputColumnNames, setInputSchema, transform
Writable reduceColumn(java.util.List<Writable> columnData)
List<Writable>
here is a single column in a reduction window,
and NOT the single row
(as is usually the case for List<Writable>
instancescolumnData
- The Writable objects for a columnjava.lang.String getColumnOutputName(java.lang.String columnInputName)
columnInputName
- Name of the column before reductionColumnMetaData getColumnOutputMetaData(java.lang.String newColumnName, ColumnMetaData columnInputMeta)
columnInputMeta
- Metadata for the column, before reduce