LocalColumnBasedRecordComparator.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 com.aliyun.odps.mapred.local.utils;

import java.util.HashMap;
import java.util.Map;

import com.aliyun.odps.Column;
import com.aliyun.odps.mapred.bridge.type.NaturalRecordComparator;
import com.aliyun.odps.mapred.conf.JobConf.SortOrder;

/**
 * 可以指定排序列的RecordComparator。排序策略是自然序。
 */
public class LocalColumnBasedRecordComparator extends NaturalRecordComparator {

  int[] selIdxs;
  SortOrder[] sortOrders;

  /**
   * ColumnBasedRecordComparator的构造方法，指定排序列的下标索引。例如指定排序列的下标索引为0，3，则比较时先用第0列比较，
   * 第0列相同时使用第3列比较。
   *
   * @param selIdxs
   *     排序列的下标索引
   * @param schema
   *     整个Record的行属性
   */
  public LocalColumnBasedRecordComparator(int[] selIdxs, Column[] schema, SortOrder[] sortOrders) {
    super(schema);
    this.selIdxs = selIdxs;
    this.sortOrders = sortOrders;
  }

  /**
   * ColumnBasedRecordComparator的构造方法，指定排序列的列名。例如指定排序列的下标索引为“word”，“count”，
   * 则比较时先用word列比较， word列相同时使用count列比较。
   *
   * @param selCols
   * @param schema
   */
  public LocalColumnBasedRecordComparator(String[] selCols, Column[] schema,
                                          SortOrder[] sortOrders) {
    super(schema);
    this.selIdxs = new int[selCols.length];
    this.sortOrders = sortOrders;
    Map<String, Integer> reverseLookupMap = new HashMap<String, Integer>();
    int i = 0;
    for (Column c : schema) {
      reverseLookupMap.put(c.getName(), i);
      i++;
    }
    i = 0;
    for (String col : selCols) {
      selIdxs[i] = reverseLookupMap.get(col);
      i++;
    }
  }

  @Override
  public int compare(Object[] l, Object[] r) {
    int result = 0;
    int index = 0;
    for (int i : selIdxs) {
      if (r.length < i) {
        if (sortOrders != null && sortOrders[index] == SortOrder.DESC) {
          return 1;
        }
        return -1;
      }
      if (l.length < i) {
        if (sortOrders != null && sortOrders[index] == SortOrder.DESC) {
          return -1;
        }
        return 1;
      }
      result = compare(l[i], r[i], comparators[i]);
      if (result != 0) {
        if (sortOrders != null && sortOrders.length == selIdxs.length
            && sortOrders[index] == SortOrder.DESC) {
          return (0 - result);
        }
        return result;
      }
      index++;
    }
    return 0;
  }

}