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casacore::TableIterator Class Reference

Iterate through a Table. More...

#include <TableIter.h>

Public Types

enum  Order {
  Ascending,
  Descending
}
 Define the possible iteration orders. More...
 
enum  Option {
  QuickSort,
  HeapSort,
  InsSort,
  ParSort,
  NoSort
}
 Define the possible sorts. More...
 

Public Member Functions

 TableIterator ()
 Create a null TableIterator object (i.e. More...
 
 TableIterator (const Table &, const String &columnName, Order=Ascending, Option=ParSort)
 Create a table iterator on the given column(s) for the given table. More...
 
 TableIterator (const Table &, const Block< String > &columnNames, Order=Ascending, Option=ParSort)
 
 TableIterator (const Table &, const Block< String > &columnNames, const Block< Int > &orders, Option=ParSort)
 Give the iteration order per column. More...
 
 TableIterator (const Table &, const Block< String > &columnNames, const Block< CountedPtr< BaseCompare > > &, const Block< Int > &orders, Option=ParSort)
 Give the iteration order per column. More...
 
 TableIterator (const TableIterator &)
 Copy constructor (copy semantics). More...
 
 ~TableIterator ()
 
TableIteratoroperator= (const TableIterator &)
 Assignment (copy semantics). More...
 
Bool isNull () const
 Test if the object is null, i.e. More...
 
void throwIfNull () const
 Throw an exception if the object is null, i.e. More...
 
void reset ()
 Reset the iterator (i.e. More...
 
Bool pastEnd () const
 Test if at the end. More...
 
void next ()
 Go to the next group. More...
 
void operator++ ()
 
void operator++ (int)
 
void copyState (const TableIterator &)
 
const StringkeyChangeAtLastNext () const
 Report Name of slowest column that changes at end of current iteration. More...
 
Table table () const
 Get the current group. More...
 

Protected Attributes

BaseTableIteratortabIterPtr_p
 
Table subTable_p
 

Detailed Description

Iterate through a Table.

Intended use:

Public interface

Review Status

Reviewed By:
UNKNOWN
Date Reviewed:
before2004/08/25

Prerequisite

Synopsis

TableIterator is a class allowing one to iterate in an arbitrary way through a table. Each iteration step returns a Table containing the result of the iteration step. It is possible to have more than one iterator on a table.

An iteration is defined by giving the columns over which to iterate. For example, take a UV data set with "axes" frequency, baseline and time. Getting all frequencies per time and baseline can be done by iterating over columns time and baseline (as shown in the example). The main iteration column must be given first. It is possible to define an iteration order per column.
It is also possible to define a compare object per column. For example, CompareIntervalReal can be used to iterate in intervals over, say, the TIME column by treating a range of values as equal (e.g. iterate in 60 seconds time intervals).

The table is sorted before doing the iteration unless TableIterator::NoSort is given.

Example

// Iterate over time and baseline (by default in ascending order).
// Time is the main iteration order.
Table t;
Table tab ("UV_Table.data");
Block<String> iv0(2);
iv0[0] = "time";
iv0[1] = "baseline";
// Create the iterator. This will prepare the first subtable.
TableIterator iter(tab, iv0);
Int nr = 0;
while (!iter.pastEnd()) {
// Get the first subtable.
// This will contain rows with equal time and baseline.
t = iter.table();
cout << t.nrow() << " ";
nr++;
// Prepare the next subtable with the next time,baseline value.
iter.next();
}
cout << endl << nr << " iteration steps" << endl;

Motivation

It is sometimes needed to access all data in a table in a grouped way; for example, all frequencies per time and baseline. This can perfectly be done with an iterator.

Definition at line 117 of file TableIter.h.

Member Enumeration Documentation

Define the possible sorts.

Enumerator
QuickSort 
HeapSort 
InsSort 
ParSort 
NoSort 

Definition at line 124 of file TableIter.h.

Define the possible iteration orders.

Enumerator
Ascending 
Descending 

Definition at line 122 of file TableIter.h.

Constructor & Destructor Documentation

casacore::TableIterator::TableIterator ( )

Create a null TableIterator object (i.e.

no iterator is attached yet). The sole purpose of this constructor is to allow construction of an array of TableIterator objects. The assignment operator can be used to make a null object reference a column. Note that sort functions, etc. will cause a segmentation fault when operating on a null object. It was felt it was too expensive to test on null over and over again. The user should use the isNull or throwIfNull function in case of doubt.

casacore::TableIterator::TableIterator ( const Table ,
const String columnName,
Order  = Ascending,
Option  = ParSort 
)

Create a table iterator on the given column(s) for the given table.

Each iteration step results in a Table containing all rows in which the values in each given column is equal. The column vector can be empty, resulting in a single iteration step giving the entire table. An iteration order can be given; it defaults to Ascending. Per column a compare object can be given to use other compare functions than the standard ones defined in Compare.h. The compare functions are used for both the sort and the iteration. The option argument makes it possible to choose from various sorting algorithms. Usually ParSort is the fastest, but for a single core machine QuickSort usually performs better. InsSort (insertion sort) should only be used if the input is almost in order. If it is known that the table is already in order, the sort step can be bypassed by giving the option TableIterator::NoSort. The default option is ParSort.

casacore::TableIterator::TableIterator ( const Table ,
const Block< String > &  columnNames,
Order  = Ascending,
Option  = ParSort 
)
casacore::TableIterator::TableIterator ( const Table ,
const Block< String > &  columnNames,
const Block< Int > &  orders,
Option  = ParSort 
)

Give the iteration order per column.


Note: If an interval comparison object like CompareIntervalReal is used, the data are sorted on the interval, not on the value; One should consider to do an explicitsort on value and no iteration sort;

casacore::TableIterator::TableIterator ( const Table ,
const Block< String > &  columnNames,
const Block< CountedPtr< BaseCompare > > &  ,
const Block< Int > &  orders,
Option  = ParSort 
)

Give the iteration order per column.

Give an optional compare object per column. A zero pointer means that the default compare function will be used.

casacore::TableIterator::TableIterator ( const TableIterator )

Copy constructor (copy semantics).

casacore::TableIterator::~TableIterator ( )

Member Function Documentation

void casacore::TableIterator::copyState ( const TableIterator )
Bool casacore::TableIterator::isNull ( ) const
inline

Test if the object is null, i.e.

does not reference a table yet. This is the case if the default constructor is used.

Definition at line 188 of file TableIter.h.

References casacore::False, tabIterPtr_p, and casacore::True.

Referenced by casacore::TableIterProxy::isNull().

const String& casacore::TableIterator::keyChangeAtLastNext ( ) const

Report Name of slowest column that changes at end of current iteration.

void casacore::TableIterator::next ( )

Go to the next group.

Referenced by operator++().

void casacore::TableIterator::operator++ ( )
inline

Definition at line 230 of file TableIter.h.

References next().

void casacore::TableIterator::operator++ ( int  )
inline

Definition at line 233 of file TableIter.h.

References next().

TableIterator& casacore::TableIterator::operator= ( const TableIterator )

Assignment (copy semantics).

Bool casacore::TableIterator::pastEnd ( ) const
inline

Test if at the end.

Definition at line 224 of file TableIter.h.

References casacore::False, casacore::Table::nrow(), subTable_p, and casacore::True.

Referenced by casa::ROCTIter::pastEnd().

void casacore::TableIterator::reset ( )

Reset the iterator (i.e.

restart iteration).

Referenced by casa::ROCTIter::reset().

Table casacore::TableIterator::table ( ) const
inline

Get the current group.

Definition at line 227 of file TableIter.h.

References subTable_p.

Referenced by casa::ROCTIter::nrow(), and casa::ROCTIter::table().

void casacore::TableIterator::throwIfNull ( ) const

Throw an exception if the object is null, i.e.

if function isNull() is True.

Member Data Documentation

Table casacore::TableIterator::subTable_p
protected

Definition at line 218 of file TableIter.h.

Referenced by pastEnd(), and table().

BaseTableIterator* casacore::TableIterator::tabIterPtr_p
protected

Definition at line 217 of file TableIter.h.

Referenced by isNull().


The documentation for this class was generated from the following file: