TableIter.h

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// # TableIter.h: Iterate through a Table
// # Copyright (C) 1994,1995,1996,1997,1999,2000
// # Associated Universities, Inc. Washington DC, USA.
// #
// # This library is free software; you can redistribute it and/or modify it
// # under the terms of the GNU Library General Public License as published by
// # the Free Software Foundation; either version 2 of the License, or (at your
// # option) any later version.
// #
// # This library is distributed in the hope that it will be useful, but WITHOUT
// # ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
// # FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Library General Public
// # License for more details.
// #
// # You should have received a copy of the GNU Library General Public License
// # along with this library; if not, write to the Free Software Foundation,
// # Inc., 675 Massachusetts Ave, Cambridge, MA 02139, USA.
// #
// # Correspondence concerning AIPS++ should be addressed as follows:
// #        Internet email: casa-feedback@nrao.edu.
// #        Postal address: AIPS++ Project Office
// #                        National Radio Astronomy Observatory
// #                        520 Edgemont Road
// #                        Charlottesville, VA 22903-2475 USA
 
#ifndef TABLES_TABLEITER_H
#define TABLES_TABLEITER_H
 
// # Includes
#include <casacore/casa/aips.h>
#include <casacore/tables/Tables/Table.h>
#include <casacore/casa/Utilities/Sort.h>
#include <casacore/casa/Utilities/Compare.h>
 
namespace casacore {  // # NAMESPACE CASACORE - BEGIN
 
// # Forward Declarations
class BaseTableIterator;
class String;
template <class T>
class Block;
 
// <summary>
// Iterate through a Table
// </summary>
 
// <use visibility=export>
 
// <reviewed reviewer="UNKNOWN" date="before2004/08/25" tests="">
// </reviewed>
 
// <prerequisite>
// # Classes you should understand before using this one.
//   <li> Table
//   <li> Sort
// </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.
// <br>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.
// </synopsis>
 
// <example>
// <srcblock>
//    // 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;
// </srcblock>
// </example>
 
// <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.
// </motivation>
 
// # <todo asof="$DATE:$">
// # A List of bugs, limitations, extensions or planned refinements.
// # </todo>
 
class TableIterator {
 public:
  // Define the possible iteration orders.
  enum Order { Ascending = Sort::Ascending, Descending = Sort::Descending };
  // Define the possible sorts.
  enum Option {
    QuickSort = Sort::QuickSort,
    HeapSort = Sort::HeapSort,
    InsSort = Sort::InsSort,
    ParSort = Sort::ParSort,
    NoSort = 64
  };
 
  // 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.
  TableIterator();
 
  // 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.
  // <group>
  TableIterator(const Table&, const String& columnName, Order = Ascending, Option = ParSort);
  TableIterator(const Table&, const Block<String>& columnNames, Order = Ascending,
                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.
  // </note>
  TableIterator(const Table&, const Block<String>& columnNames, 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.
  // If cacheIterationBoundaries is set to true then the iteration
  // boundaries computed at construction time while sorting the table
  // are used when advancing with next(). Otherwise, for each next()
  // call the comparison functions are reevaluated again to get the
  // iteration boundary. This improves performance in general but will
  // break existing applications that change the comparison objects
  // (cmpObjs) between iterations.
  TableIterator(const Table&, const Block<String>& columnNames,
                const Block<std::shared_ptr<BaseCompare>>& cmpObjs, const Block<Int>& orders,
                Option = ParSort, bool cacheIterationBoundaries = false);
  // </group>
 
  // Copy constructor (copy semantics).
  TableIterator(const TableIterator&);
 
  ~TableIterator();
 
  // Assignment (copy semantics).
  TableIterator& operator=(const TableIterator&);
 
  // Test if the object is null, i.e. does not reference a table yet.
  // This is the case if the default constructor is used.
  Bool isNull() const { return !tabIterPtr_p; }
 
  // Throw an exception if the object is null, i.e.
  // if function isNull() is True.
  void throwIfNull() const;
 
  // Reset the iterator (i.e. restart iteration).
  void reset();
 
  // Test if at the end.
  Bool pastEnd() const;
 
  // Go to the next group.
  // <group>
  void next();
  void operator++();
  void operator++(int);
  // </group>
 
  void copyState(const TableIterator&);
 
  // Report Name of slowest column that changes at end of current iteration
  const String& keyChangeAtLastNext() const;
 
  // Get the current group.
  Table table() const;
 
 protected:
  BaseTableIterator* tabIterPtr_p;
  Table subTable_p;
};
 
// # Iterator is at the end if the subtable is empty.
inline Bool TableIterator::pastEnd() const { return (subTable_p.nrow() == 0 ? True : False); }
 
inline Table TableIterator::table() const { return subTable_p; }
 
inline void TableIterator::operator++() { next(); }
 
inline void TableIterator::operator++(int) { next(); }
 
}  // namespace casacore
 
#endif