protected Map<Integer, String> toCompactString(int[][] filterMap) {
    filterMap = compactFilter(filterMap);
    if (filterMap == null) {
      return null;
    }
    Map<Integer, String> result = new LinkedHashMap<Integer, String>();
    for (int i = 0 ; i < filterMap.length; i++) {
      if (filterMap[i] == null) {
        continue;
      }
      result.put(i, Arrays.toString(filterMap[i]));
    }
    return result.isEmpty() ? null : result;
  }
@param skewKeysValuesTables
         set the table desc for storing skew keys and their corresponding
         value;
ql/src/java/org/apache/hadoop/hive/ql/plan/JoinDesc.java