uk.ac.starlink.table
Class ColumnPermutedStarTable

java.lang.Object
  extended by uk.ac.starlink.table.WrapperStarTable
      extended by uk.ac.starlink.table.ColumnPermutedStarTable
All Implemented Interfaces:
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).


Field Summary
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
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
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.
 RowSequence getRowSequence()
          Returns an object which can iterate over all the rows in the table sequentially.
 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, 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.

Specified by:
getRowSequence in interface StarTable
Overrides:
getRowSequence in class WrapperStarTable
Returns:
an object providing sequential access to the table data
Throws:
IOException - if there is an error providing access

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().

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.

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

Copyright © 2004 CLRC: Central Laboratory of the Research Councils. All rights reserved.