uk.ac.starlink.table

Class ColumnPermutedStarTable

java.lang.Object

uk.ac.starlink.table.WrapperStarTable

uk.ac.starlink.table.ColumnPermutedStarTable

All Implemented Interfaces:

Closeable, AutoCloseable, StarTable

public class ColumnPermutedStarTable
extends WrapperStarTable

Wrapper table which provides a view of a base table in which the columns are permuted. Each column in the wrapper table is a view of one in the base table. It is permitted for the wrapper to contain multiple views of the same column in the base, but note that modifying a cell in one of these will modify it in the other.

An int[] array, columnMap, is used to keep track of which columns in this table correspond to which columns in the base table; the n'th column in this table corresponds to the columnMap[n]'th column in the base table. The columnMap array may contain duplicate entries, but all its entries must be in the range 0..baseTable.getColumnCount()-1. This table will have columnMap.length entries.

One implementation decision to be made is how to implement the getRow methods on this table and on any RowSequence taken out on it. It could either invoke getRow on the base table/sequence, or invoke getCell multiple times. The performance characteristics are likely to be different for the two, though it's not obvious which will be best. In general, if this table has the same number of columns (or more) than the base table, then using getRow will be better, and if it has many fewer, then getCell will be. The user may choose between these behaviours using the readRow parameter in one of the constructors. If the other constructor (which doesn't have this argument) is used then a choice will be made on the basis of the ratio of columns in this table to the ratio of the columns in the base table (the threshold is given by READROW_FRACTION).

Author:

Mark Taylor (Starlink)

Field Summary

Fields

Modifier and Type	Field and Description
static double	READROW_FRACTION When readRow is not specified explicitly, this gives the threshold for determining how getRow methods are implemented.

Fields inherited from class uk.ac.starlink.table.WrapperStarTable

baseTable

Constructor Summary

Constructors

Constructor and Description
ColumnPermutedStarTable(StarTable baseTable, int[] columnMap) Constructs a new ColumnPermutedStarTable from a base StarTable and a columnMap array, making its own decision about how to read rows.
ColumnPermutedStarTable(StarTable baseTable, int[] columnMap, boolean readRow) Constructs a new ColumnPermutedStarTable from a base StarTable and columnMap array, with explicit instruction about how to read rows.

Method Summary

Modifier and Type	Method and Description
static ColumnPermutedStarTable	deleteColumns(StarTable baseTable, int[] icols) Returns a ColumnPermutedStarTable with selected columns deleted.
Object	getCell(long irow, int icol) Returns the contents of a given table cell.
int	getColumnCount() Returns the number of columns in this table.
ColumnInfo	getColumnInfo(int icol) Returns the object describing the data in a given column.
int[]	getColumnMap() Returns the mapping used to define the permutation of the columns of this table with respect to the base table.
Object[]	getRow(long irow) Returns the contents of a given table row.
RowAccess	getRowAccess() Returns an object which can provide random access to this table's data, if random access is implemented.
RowSequence	getRowSequence() Returns an object which can iterate over all the rows in the table sequentially.
RowSplittable	getRowSplittable() Returns an object which can iterate over all the rows in the table, but which may also be requested to split recursively for potentially parallel processing.
void	setColumnMap(int[] columnMap) Sets the mapping used to define the permutation of the columns of this table with respect to the base table.

Methods inherited from class uk.ac.starlink.table.WrapperStarTable

checkedLongToInt, close, getBaseTable, getColumnAuxDataInfos, getName, getParameterByName, getParameters, getRowCount, getURL, isRandom, setName, setParameter, setURL, toString

Methods inherited from class java.lang.Object

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

Field Detail

READROW_FRACTION

public static final double READROW_FRACTION

When readRow is not specified explicitly, this gives the threshold for determining how getRow methods are implemented. If

 getColumnCount() / getBaseTable().getColumnCount() > READROW_FRACTION
 

then the base getRow method is implemented, otherwise multiple calls of getCell are used.

See Also:

Constant Field Values

Constructor Detail

ColumnPermutedStarTable

public ColumnPermutedStarTable(StarTable baseTable,
                               int[] columnMap)

Constructs a new ColumnPermutedStarTable from a base StarTable and a columnMap array, making its own decision about how to read rows.

Parameters:

baseTable - the table on which this one is based

columnMap - array describing where each column of this table comes from in baseTable

ColumnPermutedStarTable

public ColumnPermutedStarTable(StarTable baseTable,
                               int[] columnMap,
                               boolean readRow)

Constructs a new ColumnPermutedStarTable from a base StarTable and columnMap array, with explicit instruction about how to read rows.

Parameters:

baseTable - the table on which this one is based

columnMap - array describing where each column of this table comes from in baseTable

readRow - true if the readRow implementations should invoke readRow on the base table, false if they should use readCell instead

Method Detail

getColumnMap

public int[] getColumnMap()

Returns the mapping used to define the permutation of the columns of this table with respect to the base table.

Returns:

column permutation map

setColumnMap

public void setColumnMap(int[] columnMap)

Sets the mapping used to define the permutation of the columns of this table with respect to the base table.

Parameters:

columnMap - column permutation map

getColumnCount

public int getColumnCount()

Description copied from interface: StarTable

Returns the number of columns in this table.

Specified by:

getColumnCount in interface StarTable

Overrides:

getColumnCount in class WrapperStarTable

Returns:

the number of columns

getColumnInfo

public ColumnInfo getColumnInfo(int icol)

Description copied from interface: StarTable

Returns the object describing the data in a given column.

Specified by:

getColumnInfo in interface StarTable

Overrides:

getColumnInfo in class WrapperStarTable

Parameters:

icol - the column for which header information is required

Returns:

a ValueInfo object for column icol

getRowSequence

public RowSequence getRowSequence()
                           throws IOException

Description copied from interface: StarTable

Returns an object which can iterate over all the rows in the table sequentially. Each such returned object is safe for use within a single thread, but not in general from multiple threads concurrently.

Specified by:

getRowSequence in interface StarTable

Overrides:

getRowSequence in class WrapperStarTable

Returns:

new RowSequence

Throws:

IOException - if there is an error providing access

getRowAccess

public RowAccess getRowAccess()
                       throws IOException

Description copied from interface: StarTable

Returns an object which can provide random access to this table's data, if random access is implemented. Each such returned object is safe for use within a single thread, but not in general from multiple threads concurrently.

Specified by:

getRowAccess in interface StarTable

Overrides:

getRowAccess in class WrapperStarTable

Returns:

new RowAccess

Throws:

IOException - if there is an error setting up access

getRowSplittable

public RowSplittable getRowSplittable()
                               throws IOException

Description copied from interface: StarTable

Returns an object which can iterate over all the rows in the table, but which may also be requested to split recursively for potentially parallel processing.

The return value must be non-null, and may provide splitting arrangements specially appropriate for the implementation. If this table 'wraps' an upstream table, it is usually best to base the implementation on calls to the the upstream getRowSplittable method, so that upstream policy about how to divide up the table is respected. However, implementations without special requirements may return Tables.getDefaultRowSplittable(this).

Specified by:

getRowSplittable in interface StarTable

Overrides:

getRowSplittable in class WrapperStarTable

Returns:

new RowSplittable

Throws:

IOException

See Also:

RowRunner

getCell

public Object getCell(long irow,
                      int icol)
               throws IOException

Description copied from interface: StarTable

Returns the contents of a given table cell. The class of the returned object should be the same as, or a subclass of, the class returned by getColumnInfo(icol).getContentClass().

This method is safe for concurrent use from multiple threads, but in general it is recommended to use a RowAccess instead.

Specified by:

getCell in interface StarTable

Overrides:

getCell in class WrapperStarTable

Parameters:

irow - the index of the cell's row

icol - the index of the cell's column

Returns:

the contents of this cell

Throws:

IOException - if there is an error reading the data

getRow

public Object[] getRow(long irow)
                throws IOException

Description copied from interface: StarTable

Returns the contents of a given table row. The returned value is equivalent to an array formed of all the objects returned by getCell(irow,icol) for all the columns icol in sequence.

This method is safe for concurrent use from multiple threads, but in general it is recommended to use a RowAccess instead.

Specified by:

getRow in interface StarTable

Overrides:

getRow in class WrapperStarTable

Parameters:

irow - the index of the row to retrieve

Returns:

an array of the objects in each cell in row irow

Throws:

IOException - if there is an error reading the data

deleteColumns

public static ColumnPermutedStarTable deleteColumns(StarTable baseTable,
                                                    int[] icols)

Returns a ColumnPermutedStarTable with selected columns deleted. This utility method simply works out a permutation map which corresponds to deletion of the columns indexed by the elements of the icols array and passes it to the constructor. A single column index may harmlessly be listed multiple times in the icols array. It is not permitted for any element of icols to be less than zero or greater or equal than the number of columns in baseTable.

Parameters:

baseTable - table whose columns are to be deleted

icols - array with elements listing the column indices which are to be removed