src/main/java/org/apache/sysds/runtime/compress/colgroup/ColGroupSDC.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.apache.sysds.runtime.compress.colgroup;

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import java.util.Arrays;

import org.apache.sysds.runtime.DMLRuntimeException;
import org.apache.sysds.runtime.compress.DMLCompressionException;
import org.apache.sysds.runtime.compress.colgroup.dictionary.ADictionary;
import org.apache.sysds.runtime.compress.colgroup.dictionary.Dictionary;
import org.apache.sysds.runtime.compress.colgroup.dictionary.DictionaryFactory;
import org.apache.sysds.runtime.compress.colgroup.dictionary.MatrixBlockDictionary;
import org.apache.sysds.runtime.compress.colgroup.indexes.ColIndexFactory;
import org.apache.sysds.runtime.compress.colgroup.indexes.IColIndex;
import org.apache.sysds.runtime.compress.colgroup.mapping.AMapToData;
import org.apache.sysds.runtime.compress.colgroup.mapping.MapToFactory;
import org.apache.sysds.runtime.compress.colgroup.offset.AIterator;
import org.apache.sysds.runtime.compress.colgroup.offset.AOffset;
import org.apache.sysds.runtime.compress.colgroup.offset.AOffset.OffsetSliceInfo;
import org.apache.sysds.runtime.compress.colgroup.offset.OffsetFactory;
import org.apache.sysds.runtime.compress.colgroup.scheme.ICLAScheme;
import org.apache.sysds.runtime.compress.cost.ComputationCostEstimator;
import org.apache.sysds.runtime.compress.estim.encoding.EncodingFactory;
import org.apache.sysds.runtime.compress.estim.encoding.IEncode;
import org.apache.sysds.runtime.functionobjects.Builtin;
import org.apache.sysds.runtime.instructions.cp.CM_COV_Object;
import org.apache.sysds.runtime.matrix.data.MatrixBlock;
import org.apache.sysds.runtime.matrix.operators.BinaryOperator;
import org.apache.sysds.runtime.matrix.operators.CMOperator;
import org.apache.sysds.runtime.matrix.operators.ScalarOperator;
import org.apache.sysds.runtime.matrix.operators.UnaryOperator;

/**
 * Column group that sparsely encodes the dictionary values. The idea is that all values is encoded with indexes except
 * the most common one. the most common one can be inferred by not being included in the indexes.
 * 
 * This column group is handy in cases where sparse unsafe operations is executed on very sparse columns. Then the zeros
 * would be materialized in the group without any overhead.
 */
public class ColGroupSDC extends ASDC implements IMapToDataGroup {
	private static final long serialVersionUID = 769993538831949086L;

	/** Pointers to row indexes in the dictionary. */
	protected final AMapToData _data;
	/** The default value stored in this column group */
	protected final double[] _defaultTuple;

	protected ColGroupSDC(IColIndex colIndices, int numRows, ADictionary dict, double[] defaultTuple, AOffset offsets,
		AMapToData data, int[] cachedCounts) {
		super(colIndices, numRows, dict, offsets, cachedCounts);
		if(data.getUnique() != dict.getNumberOfValues(colIndices.size())) {
			if(data.getUnique() != data.getMax())
				throw new DMLCompressionException(
					"Invalid unique count compared to actual: " + data.getUnique() + " " + data.getMax());
			throw new DMLCompressionException("Invalid construction of SDC group: number uniques: " + data.getUnique()
				+ " vs." + dict.getNumberOfValues(colIndices.size()));
		}
		if(defaultTuple.length != colIndices.size())
			throw new DMLCompressionException("Invalid construction of SDC group");

		_data = data;
		_defaultTuple = defaultTuple;
	}

	public static AColGroup create(IColIndex colIndices, int numRows, ADictionary dict, double[] defaultTuple,
		AOffset offsets, AMapToData data, int[] cachedCounts) {
		final boolean allZero = ColGroupUtils.allZero(defaultTuple);
		if(dict == null && allZero)
			return new ColGroupEmpty(colIndices);
		else if(dict == null || dict.getNumberOfValues(colIndices.size()) == 1)
			return ColGroupSDCSingle.create(colIndices, numRows, dict, defaultTuple, offsets, null);
		else if(allZero)
			return ColGroupSDCZeros.create(colIndices, numRows, dict, offsets, data, cachedCounts);
		else if(data.getUnique() == 1) {
			MatrixBlock mb = dict.getMBDict(colIndices.size()).getMatrixBlock().slice(0, 0);
			return ColGroupSDCSingle.create(colIndices, numRows, MatrixBlockDictionary.create(mb), defaultTuple, offsets,
				null);
		}
		else
			return new ColGroupSDC(colIndices, numRows, dict, defaultTuple, offsets, data, cachedCounts);
	}

	public AColGroup sparsifyFOR() {
		return ColGroupSDCFOR.sparsifyFOR(this);
	}

	@Override
	public CompressionType getCompType() {
		return CompressionType.SDC;
	}

	@Override
	public ColGroupType getColGroupType() {
		return ColGroupType.SDC;
	}

	@Override
	public double[] getDefaultTuple() {
		return _defaultTuple;
	}

	@Override
	public AMapToData getMapToData() {
		return _data;
	}

	@Override
	public double getIdx(int r, int colIdx) {
		final AIterator it = _indexes.getIterator(r);
		if(it == null || it.value() != r)
			return _defaultTuple[colIdx];
		else
			return _dict.getValue(_data.getIndex(it.getDataIndex()), colIdx, _colIndexes.size());

	}

	@Override
	protected double[] preAggSumRows() {
		return _dict.sumAllRowsToDoubleWithDefault(_defaultTuple);
	}

	@Override
	protected double[] preAggSumSqRows() {
		return _dict.sumAllRowsToDoubleSqWithDefault(_defaultTuple);
	}

	@Override
	protected double[] preAggProductRows() {
		return _dict.productAllRowsToDoubleWithDefault(_defaultTuple);
	}

	@Override
	protected double[] preAggBuiltinRows(Builtin builtin) {
		return _dict.aggregateRowsWithDefault(builtin, _defaultTuple);
	}

	@Override
	protected double computeMxx(double c, Builtin builtin) {
		double ret = _dict.aggregate(c, builtin);
		for(int i = 0; i < _defaultTuple.length; i++)
			ret = builtin.execute(ret, _defaultTuple[i]);
		return ret;
	}

	@Override
	protected void computeColMxx(double[] c, Builtin builtin) {
		_dict.aggregateCols(c, builtin, _colIndexes);
		for(int x = 0; x < _colIndexes.size(); x++)
			c[_colIndexes.get(x)] = builtin.execute(c[_colIndexes.get(x)], _defaultTuple[x]);
	}

	@Override
	protected void computeRowSums(double[] c, int rl, int ru, double[] preAgg) {
		computeRowSums(c, rl, ru, preAgg, _data, _indexes, _numRows);
	}

	protected static final void computeRowSums(double[] c, int rl, int ru, double[] preAgg, AMapToData data,
		AOffset indexes, int nRows) {
		int r = rl;
		final AIterator it = indexes.getIterator(rl);
		final double def = preAgg[preAgg.length - 1];
		if(it != null) {

			if(it.value() > ru)
				indexes.cacheIterator(it, ru);
			else if(ru > indexes.getOffsetToLast()) {
				final int maxId = data.size() - 1;

				while(true) {
					if(it.value() == r) {
						c[r] += preAgg[data.getIndex(it.getDataIndex())];
						if(it.getDataIndex() < maxId)
							it.next();
						else {
							r++;
							break;
						}
					}
					else
						c[r] += def;
					r++;
				}
			}
			else {
				while(r < ru) {
					if(it.value() == r) {
						c[r++] += preAgg[data.getIndex(it.getDataIndex())];
						it.next();
					}
					else
						c[r++] += def;
				}
				indexes.cacheIterator(it, ru);
			}
		}

		while(r < ru)
			c[r++] += def;
	}

	@Override
	protected void computeRowMxx(double[] c, Builtin builtin, int rl, int ru, double[] preAgg) {
		computeRowMxx(c, builtin, rl, ru, preAgg, _data, _indexes, _numRows, preAgg[preAgg.length - 1]);
	}

	protected static final void computeRowMxx(double[] c, Builtin builtin, int rl, int ru, double[] preAgg,
		AMapToData data, AOffset indexes, int nRows, double def) {
		int r = rl;
		final AIterator it = indexes.getIterator(rl);
		if(it != null) {
			if(it.value() > ru)
				indexes.cacheIterator(it, ru);
			else if(ru > indexes.getOffsetToLast()) {
				final int maxId = data.size() - 1;
				while(true) {
					if(it.value() == r) {
						c[r] = builtin.execute(c[r], preAgg[data.getIndex(it.getDataIndex())]);
						if(it.getDataIndex() < maxId)
							it.next();
						else {
							r++;
							break;
						}
					}
					else
						c[r] = builtin.execute(c[r], def);
					r++;
				}
			}
			else {
				while(r < ru) {
					if(it.value() == r) {
						c[r] = builtin.execute(c[r], preAgg[data.getIndex(it.getDataIndex())]);
						it.next();
					}
					else
						c[r] = builtin.execute(c[r], def);
					r++;
				}
				indexes.cacheIterator(it, ru);
			}
		}

		while(r < ru) {
			c[r] = builtin.execute(c[r], def);
			r++;
		}

	}

	@Override
	protected void computeSum(double[] c, int nRows) {
		super.computeSum(c, nRows);
		int count = _numRows - _data.size();
		for(int x = 0; x < _defaultTuple.length; x++)
			c[0] += _defaultTuple[x] * count;
	}

	@Override
	public void computeColSums(double[] c, int nRows) {
		super.computeColSums(c, nRows);
		int count = _numRows - _data.size();
		for(int x = 0; x < _colIndexes.size(); x++)
			c[_colIndexes.get(x)] += _defaultTuple[x] * count;
	}

	@Override
	protected void computeSumSq(double[] c, int nRows) {
		super.computeSumSq(c, nRows);
		int count = _numRows - _data.size();
		for(int x = 0; x < _colIndexes.size(); x++)
			c[0] += _defaultTuple[x] * _defaultTuple[x] * count;
	}

	@Override
	protected void computeColSumsSq(double[] c, int nRows) {
		super.computeColSumsSq(c, nRows);
		int count = _numRows - _data.size();
		for(int x = 0; x < _colIndexes.size(); x++)
			c[_colIndexes.get(x)] += _defaultTuple[x] * _defaultTuple[x] * count;
	}

	@Override
	protected void computeProduct(double[] c, int nRows) {
		final int count = _numRows - _data.size();
		_dict.productWithDefault(c, getCounts(), _defaultTuple, count);
	}

	@Override
	protected void computeColProduct(double[] c, int nRows) {
		super.computeColProduct(c, nRows);
		final int count = _numRows - _data.size();
		for(int x = 0; x < _colIndexes.size(); x++) {
			double v = c[_colIndexes.get(x)];
			c[_colIndexes.get(x)] = v != 0 ? v * Math.pow(_defaultTuple[x], count) : 0;
		}
	}

	@Override
	protected void computeRowProduct(double[] c, int rl, int ru, double[] preAgg) {
		computeRowProduct(c, rl, ru, preAgg, _data, _indexes, _numRows);
	}

	protected static final void computeRowProduct(double[] c, int rl, int ru, double[] preAgg, AMapToData data,
		AOffset indexes, int nRows) {
		int r = rl;
		final AIterator it = indexes.getIterator(rl);
		final double def = preAgg[preAgg.length - 1];
		if(it != null) {

			if(it.value() > ru)
				indexes.cacheIterator(it, ru);
			else if(ru > indexes.getOffsetToLast()) {
				final int maxId = data.size() - 1;
				while(true) {
					if(it.value() == r) {
						c[r] *= preAgg[data.getIndex(it.getDataIndex())];
						if(it.getDataIndex() < maxId)
							it.next();
						else {
							r++;
							break;
						}
					}
					else
						c[r] *= def;
					r++;
				}
			}
			else {
				while(r < ru) {
					if(it.value() == r) {
						c[r] *= preAgg[data.getIndex(it.getDataIndex())];
						it.next();
					}
					else
						c[r] *= def;
					r++;
				}
				indexes.cacheIterator(it, ru);
			}
		}

		while(r < ru) {
			c[r] *= def;
			r++;
		}
	}

	@Override
	public int[] getCounts(int[] counts) {
		return _data.getCounts(counts);
	}

	@Override
	public long getNumberNonZeros(int nRows) {
		long c = super.getNumberNonZeros(nRows);
		int count = _numRows - _data.size();
		for(int x = 0; x < _colIndexes.size(); x++)
			c += _defaultTuple[x] != 0 ? count : 0;
		return c;
	}

	@Override
	public long estimateInMemorySize() {
		long size = super.estimateInMemorySize();
		size += _indexes.getInMemorySize();
		size += _data.getInMemorySize();
		size += 8 * _colIndexes.size();
		return size;
	}

	@Override
	public AColGroup scalarOperation(ScalarOperator op) {
		final double[] newDefaultTuple = new double[_defaultTuple.length];
		for(int i = 0; i < _defaultTuple.length; i++)
			newDefaultTuple[i] = op.executeScalar(_defaultTuple[i]);
		final ADictionary nDict = _dict.applyScalarOp(op);
		return create(_colIndexes, _numRows, nDict, newDefaultTuple, _indexes, _data, getCachedCounts());
	}

	@Override
	public AColGroup unaryOperation(UnaryOperator op) {
		final double[] newDefaultTuple = new double[_defaultTuple.length];
		for(int i = 0; i < _defaultTuple.length; i++)
			newDefaultTuple[i] = op.fn.execute(_defaultTuple[i]);
		final ADictionary nDict = _dict.applyUnaryOp(op);
		return create(_colIndexes, _numRows, nDict, newDefaultTuple, _indexes, _data, getCachedCounts());
	}

	@Override
	public AColGroup binaryRowOpLeft(BinaryOperator op, double[] v, boolean isRowSafe) {
		final double[] newDefaultTuple = new double[_defaultTuple.length];
		for(int i = 0; i < _defaultTuple.length; i++)
			newDefaultTuple[i] = op.fn.execute(v[_colIndexes.get(i)], _defaultTuple[i]);
		final ADictionary newDict = _dict.binOpLeft(op, v, _colIndexes);
		return create(_colIndexes, _numRows, newDict, newDefaultTuple, _indexes, _data, getCachedCounts());
	}

	@Override
	public AColGroup binaryRowOpRight(BinaryOperator op, double[] v, boolean isRowSafe) {
		final double[] newDefaultTuple = new double[_defaultTuple.length];
		for(int i = 0; i < _defaultTuple.length; i++)
			newDefaultTuple[i] = op.fn.execute(_defaultTuple[i], v[_colIndexes.get(i)]);
		final ADictionary newDict = _dict.binOpRight(op, v, _colIndexes);
		return create(_colIndexes, _numRows, newDict, newDefaultTuple, _indexes, _data, getCachedCounts());
	}

	@Override
	public void write(DataOutput out) throws IOException {
		super.write(out);
		_indexes.write(out);
		_data.write(out);
		for(double d : _defaultTuple)
			out.writeDouble(d);
	}

	public static ColGroupSDC read(DataInput in, int nRows) throws IOException {
		IColIndex cols = ColIndexFactory.read(in);
		ADictionary dict = DictionaryFactory.read(in);
		AOffset indexes = OffsetFactory.readIn(in);
		AMapToData data = MapToFactory.readIn(in);
		double[] defaultTuple = ColGroupIO.readDoubleArray(cols.size(), in);
		return new ColGroupSDC(cols, nRows, dict, defaultTuple, indexes, data, null);
	}

	@Override
	public long getExactSizeOnDisk() {
		long ret = super.getExactSizeOnDisk();
		ret += _data.getExactSizeOnDisk();
		ret += _indexes.getExactSizeOnDisk();
		ret += 8 * _colIndexes.size(); // _default tuple values.
		return ret;
	}

	@Override
	public AColGroup replace(double pattern, double replace) {
		ADictionary replaced = _dict.replace(pattern, replace, _colIndexes.size());
		double[] newDefaultTuple = new double[_defaultTuple.length];
		for(int i = 0; i < _defaultTuple.length; i++)
			newDefaultTuple[i] = _defaultTuple[i] == pattern ? replace : _defaultTuple[i];

		return create(_colIndexes, _numRows, replaced, newDefaultTuple, _indexes, _data, getCachedCounts());
	}

	@Override
	public AColGroup extractCommon(double[] constV) {
		for(int i = 0; i < _colIndexes.size(); i++)
			constV[_colIndexes.get(i)] += _defaultTuple[i];

		ADictionary subtractedDict = _dict.subtractTuple(_defaultTuple);
		return ColGroupSDCZeros.create(_colIndexes, _numRows, subtractedDict, _indexes, _data, getCounts());
	}

	public AColGroup subtractDefaultTuple() {
		ADictionary subtractedDict = _dict.subtractTuple(_defaultTuple);
		return ColGroupSDCZeros.create(_colIndexes, _numRows, subtractedDict, _indexes, _data, getCounts());
	}

	@Override
	public CM_COV_Object centralMoment(CMOperator op, int nRows) {
		return _dict.centralMomentWithDefault(op.fn, getCounts(), _defaultTuple[0], nRows);
	}

	@Override
	public AColGroup rexpandCols(int max, boolean ignore, boolean cast, int nRows) {
		ADictionary d = _dict.rexpandCols(max, ignore, cast, _colIndexes.size());
		return rexpandCols(max, ignore, cast, nRows, d, _indexes, _data, getCachedCounts(), (int) _defaultTuple[0]);
	}

	protected static AColGroup rexpandCols(int max, boolean ignore, boolean cast, int nRows, ADictionary d,
		AOffset indexes, AMapToData data, int[] counts, int def) {

		if(d == null) {
			if(def <= 0 || def > max)
				return ColGroupEmpty.create(max);
			else {
				double[] retDef = new double[max];
				retDef[((int) def) - 1] = 1;
				return ColGroupSDCSingle.create(ColIndexFactory.create(max), nRows, Dictionary.create(new double[max]),
					retDef, indexes, null);
			}
		}
		else {
			final IColIndex outCols = ColIndexFactory.create(max);
			if(def <= 0) {
				if(ignore)
					return ColGroupSDCZeros.create(outCols, nRows, d, indexes, data, counts);
				else
					throw new DMLRuntimeException("Invalid content of zero in rexpand");
			}
			else if(def > max)
				return ColGroupSDCZeros.create(outCols, nRows, d, indexes, data, counts);
			else {
				double[] retDef = new double[max];
				retDef[((int) def) - 1] = 1;
				return ColGroupSDC.create(outCols, nRows, d, retDef, indexes, data, counts);
			}
		}
	}

	@Override
	public double getCost(ComputationCostEstimator e, int nRows) {
		final int nVals = getNumValues();
		final int nCols = getNumCols();
		final int nRowsScanned = _data.size();
		return e.getCost(nRows, nRowsScanned, nCols, nVals, _dict.getSparsity());
	}

	@Override
	protected AColGroup sliceMultiColumns(int idStart, int idEnd, IColIndex outputCols) {
		ADictionary retDict = _dict.sliceOutColumnRange(idStart, idEnd, _colIndexes.size());
		final double[] newDef = new double[idEnd - idStart];
		for(int i = idStart, j = 0; i < idEnd; i++, j++)
			newDef[j] = _defaultTuple[i];
		return create(outputCols, _numRows, retDict, newDef, _indexes, _data, getCounts());
	}

	@Override
	protected AColGroup sliceSingleColumn(int idx) {
		final IColIndex retIndexes = ColIndexFactory.create(1);
		if(_colIndexes.size() == 1) // early abort, only single column already.
			return create(retIndexes, _numRows, _dict, _defaultTuple, _indexes, _data, getCounts());
		final double[] newDef = new double[] {_defaultTuple[idx]};
		final ADictionary retDict = _dict.sliceOutColumnRange(idx, idx + 1, _colIndexes.size());
		return create(retIndexes, _numRows, retDict, newDef, _indexes, _data, getCounts());
	}

	@Override
	public boolean containsValue(double pattern) {
		if(_dict.containsValue(pattern))
			return true;
		for(double v : _defaultTuple)
			if(v == pattern)
				return true;
		return false;
	}

	@Override
	public double[] getCommon() {
		return _defaultTuple;
	}

	@Override
	protected AColGroup allocateRightMultiplicationCommon(double[] common, IColIndex colIndexes, ADictionary preAgg) {
		return create(colIndexes, _numRows, preAgg, common, _indexes, _data, getCachedCounts());
	}

	@Override
	public AColGroup sliceRows(int rl, int ru) {

		if(ru > _numRows)
			throw new DMLRuntimeException("Invalid row range");
		OffsetSliceInfo off = _indexes.slice(rl, ru);
		if(off.lIndex == -1)
			return ColGroupConst.create(_colIndexes, Dictionary.create(_defaultTuple));
		AMapToData newData = _data.slice(off.lIndex, off.uIndex);
		return create(_colIndexes, ru - rl, _dict, _defaultTuple, off.offsetSlice, newData, null);
	}

	@Override
	protected AColGroup copyAndSet(IColIndex colIndexes, ADictionary newDictionary) {
		return create(colIndexes, _numRows, newDictionary, _defaultTuple, _indexes, _data, getCachedCounts());
	}

	@Override
	public AColGroup append(AColGroup g) {
		if(g instanceof ColGroupSDC && g.getColIndices().equals(_colIndexes)) {
			final ColGroupSDC gSDC = (ColGroupSDC) g;
			if(Arrays.equals(_defaultTuple, gSDC._defaultTuple) && gSDC._dict.equals(_dict)) {
				final AMapToData nd = _data.append(gSDC._data);
				final AOffset ofd = _indexes.append(gSDC._indexes, getNumRows());
				return create(_colIndexes, _numRows + gSDC._numRows, _dict, _defaultTuple, ofd, nd, null);
			}
		}
		return null;
	}

	@Override
	public AColGroup appendNInternal(AColGroup[] g) {
		int sumRows = getNumRows();
		for(int i = 1; i < g.length; i++) {
			if(!_colIndexes.equals(g[i]._colIndexes)) {
				LOG.warn("Not same columns therefore not appending \n" + _colIndexes + "\n\n" + g[i]._colIndexes);
				return null;
			}

			if(!(g[i] instanceof ColGroupSDC)) {
				LOG.warn("Not SDC but " + g[i].getClass().getSimpleName());
				return null;
			}

			final ColGroupSDC gc = (ColGroupSDC) g[i];
			if(!gc._dict.equals(_dict)) {
				LOG.warn("Not same Dictionaries therefore not appending \n" + _dict + "\n\n" + gc._dict);
				return null;
			}
			sumRows += gc.getNumRows();
		}
		AMapToData nd = _data.appendN(Arrays.copyOf(g, g.length, IMapToDataGroup[].class));
		AOffset no = _indexes.appendN(Arrays.copyOf(g, g.length, AOffsetsGroup[].class), getNumRows());

		return create(_colIndexes, sumRows, _dict, _defaultTuple, no, nd, null);
	}

	@Override
	public ICLAScheme getCompressionScheme() {
		return null;
	}

	@Override
	public AColGroup recompress() {
		return this;
	}

	@Override
	public IEncode getEncoding() {
		return EncodingFactory.create(_data, _indexes, _numRows);
	}

	@Override
	protected AColGroup fixColIndexes(IColIndex newColIndex, int[] reordering) {
		return ColGroupSDC.create(newColIndex, getNumRows(), _dict.reorder(reordering),
			ColGroupUtils.reorderDefault(_defaultTuple, reordering), _indexes, _data, getCachedCounts());
	}

	@Override
	public boolean sameIndexStructure(AColGroupCompressed that) {
		if(that instanceof ColGroupSDCZeros) {
			ColGroupSDCZeros th = (ColGroupSDCZeros) that;
			return th._indexes == _indexes && th._data == _data;
		}
		else if(that instanceof ColGroupSDC) {
			ColGroupSDC th = (ColGroupSDC) that;
			return th._indexes == _indexes && th._data == _data;
		}
		else
			return false;
	}

	@Override
	public int getNumberOffsets() {
		return _data.size();
	}

	@Override
	public String toString() {
		StringBuilder sb = new StringBuilder();
		sb.append(super.toString());
		sb.append(String.format("\n%15s", "Default: "));
		sb.append(Arrays.toString(_defaultTuple));
		sb.append(String.format("\n%15s", "Indexes: "));
		sb.append(_indexes.toString());
		sb.append(String.format("\n%15s", "Data: "));
		sb.append(_data.toString());
		return sb.toString();
	}
}