uk.ac.starlink.ttools.task

Class TableGroup

java.lang.Object

uk.ac.starlink.ttools.task.ConsumerTask

uk.ac.starlink.ttools.task.SingleMapperTask

uk.ac.starlink.ttools.task.TableGroup

All Implemented Interfaces:

Task

public class TableGroup
extends SingleMapperTask

Task for performing aggregation operations on groups of rows of an input table.

Since:

17 Nov 2022

Author:

Mark Taylor

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	TableGroup.AggSpec Defines the aggregation that should be done to form an output column.

Field Summary

Fields

Modifier and Type	Field and Description
static char	AGGCOL_DELIM Delimiter character for aggcol parameter entries.

Constructor Summary

Constructors

Constructor and Description
TableGroup() Constructor.

Method Summary

Modifier and Type	Method and Description
static StarTable	aggregateRows(StarTable inTable, String[] keyExprs, TableGroup.AggSpec[] aggSpecs, RowRunner runner, boolean isSort, boolean isCache) Does the aggregation work.
TableProducer	createProducer(Environment env) Returns an object which can produce the effective output table which will be consumed by this task.
static TableGroup.AggSpec	parseAggSpec(String aggSpecTxt, char delimChr) Parses an aggregate specification string to an AggSpec.

Methods inherited from class uk.ac.starlink.ttools.task.SingleMapperTask

createInputProducer, getInputFilterParameter, getInputTableParameter

Methods inherited from class uk.ac.starlink.ttools.task.ConsumerTask

createExecutable, createProducer, getIdentity, getOutputMode, getParameterList, getParameters, getPurpose

Methods inherited from class java.lang.Object

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

Field Detail

AGGCOL_DELIM

public static final char AGGCOL_DELIM

Delimiter character for aggcol parameter entries.

See Also:

Constant Field Values

Constructor Detail

TableGroup

public TableGroup()

Constructor.

Method Detail

createProducer

public TableProducer createProducer(Environment env)
                             throws TaskException

Description copied from class: ConsumerTask

Returns an object which can produce the effective output table which will be consumed by this task. The table produced by the resulting producer can be fed to the ConsumerTask.getIdentity(uk.ac.starlink.table.StarTable) method.

Specified by:

createProducer in class ConsumerTask

Parameters:

env - execution environment

Returns:

table producer

Throws:

TaskException

parseAggSpec

public static TableGroup.AggSpec parseAggSpec(String aggSpecTxt,
                                              char delimChr)
                                       throws UsageException

Parses an aggregate specification string to an AggSpec. The returned value can be passed to the aggregateRows method. The input string is as documented of the form "<input-expr><delim><aggregator-name>[<delim><output-name>]". If the input string cannot be so parsed, a UsageException with an informative message is thrown.

Parameters:

aggSpecTxt - text specifying aggregated output

delimChr - delimiter character between the three parts of the expression

Returns:

parsed specification

Throws:

UsageException

aggregateRows

public static StarTable aggregateRows(StarTable inTable,
                                      String[] keyExprs,
                                      TableGroup.AggSpec[] aggSpecs,
                                      RowRunner runner,
                                      boolean isSort,
                                      boolean isCache)
                               throws IOException,
                                      TaskException

Does the aggregation work.

Parameters:

inTable - input table

keyExprs - input table values that define grouping

aggSpecs - specification for output aggregated columns

runner - row runner

isSort - if true, output table is sorted before return (where possible)

isCache - if true, output table is cached before return

Returns:

output table containing aggregated values

Throws:

IOException

TaskException