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Declarative Machine Learning
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/*
 * 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.sysml.runtime.matrix.data;

import java.util.Iterator;

/**
 * Iterator for external use of matrix blocks in sparse representation.
 * It allows to linearly iterate only over non-zero values which is
 * important for sparse safe operations.
 * 
 */
public class SparseRowsIterator implements Iterator
{
	
	private int rlen = 0;
	private SparseRow[] sparseRows = null;
	private int curRow = -1;
	private int curColIndex = -1;
	private int[] colIndexes = null;
	private double[] values = null;
	private boolean nothingLeft = false;
	private IJV retijv = new IJV();

	//allow initialization from package or subclasses
	protected SparseRowsIterator(int nrows, SparseRow[] mtx)
	{
		rlen=nrows;
		sparseRows=mtx;
		curRow=0;
		
		if(sparseRows==null)
			nothingLeft=true;
		else
			findNextNonZeroRow();
	}
	
	//allow initialization from package or subclasses
	protected SparseRowsIterator(int currow, int nrows, SparseRow[] mtx)
	{
		rlen=nrows;
		sparseRows=mtx;
		curRow=currow;
		
		if(sparseRows==null)
			nothingLeft=true;
		else
			findNextNonZeroRow();
	}
	
	@Override
	public boolean hasNext() {
		if(nothingLeft)
			return false;
		else
			return true;
	}

	@Override
	public IJV next( ) {
		retijv.set(curRow, colIndexes[curColIndex], values[curColIndex]);
		curColIndex++;
		if(curColIndex>=sparseRows[curRow].size())
		{
			curRow++;
			findNextNonZeroRow();
		}
		return retijv;
	}

	@Override
	public void remove() {
		throw new RuntimeException("SparseCellIterator.remove should not be called!");
		
	}		
	
	/**
	 * 
	 */
	private void findNextNonZeroRow() 
	{
		while(curRow=Math.min(rlen, sparseRows.length))
			nothingLeft=true;
		else
		{
			curColIndex=0;
			colIndexes=sparseRows[curRow].getIndexContainer();
			values=sparseRows[curRow].getValueContainer();
		}
	}
}