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java.lang.Object | +--uk.ac.starlink.table.WrapperStarTable | +--uk.ac.starlink.table.ColumnPermutedStarTable
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 |
Methods inherited from class java.lang.Object |
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Field Detail |
public static final double READROW_FRACTION
getColumnCount() / getBaseTable().getColumnCount() > READROW_FRACTIONthen the base getRow method is implemented, otherwise multiple calls of getCell are used.
Constructor Detail |
public ColumnPermutedStarTable(StarTable baseTable, int[] columnMap)
baseTable
- the table on which this one is basedcolumnMap
- array describing where each column of this table
comes from in baseTablepublic ColumnPermutedStarTable(StarTable baseTable, int[] columnMap, boolean readRow)
baseTable
- the table on which this one is basedcolumnMap
- array describing where each column of this table
comes from in baseTablereadRow
- true if the readRow implementations should
invoke readRow on the base table, false if they
should use readCell insteadMethod Detail |
public int[] getColumnMap()
public void setColumnMap(int[] columnMap)
columnMap
- column permutation mappublic int getColumnCount()
StarTable
getColumnCount
in interface StarTable
getColumnCount
in class WrapperStarTable
public ColumnInfo getColumnInfo(int icol)
StarTable
getColumnInfo
in interface StarTable
getColumnInfo
in class WrapperStarTable
icol
- the column for which header information is required
public RowSequence getRowSequence() throws IOException
StarTable
getRowSequence
in interface StarTable
getRowSequence
in class WrapperStarTable
IOException
- if there is an error providing accesspublic Object getCell(long irow, int icol) throws IOException
StarTable
getCell
in interface StarTable
getCell
in class WrapperStarTable
irow
- the index of the cell's rowicol
- the index of the cell's column
IOException
- if there is an error reading the datapublic Object[] getRow(long irow) throws IOException
StarTable
getRow
in interface StarTable
getRow
in class WrapperStarTable
irow
- the index of the row to retrieve
IOException
- if there is an error reading the datapublic static ColumnPermutedStarTable deleteColumns(StarTable baseTable, int[] icols)
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
.
baseTable
- table whose columns are to be deletedicols
- array with elements listing the column indices
which are to be removed
|
Copyright © 2004 CLRC: Central Laboratory of the Research Councils. All rights reserved. | |||||||||
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