code: private Instance[] readInstance(String corpus, FeatureMap featureMap)
      {
          IOUtil.LineIterator lineIterator = new IOUtil.LineIterator(corpus);
          List<Instance> instanceList = new LinkedList<Instance>();
          for (String line : lineIterator)
          {
              String[] cells = line.split(",");
              String text = cells[0], label = cells[1];
              List<Integer> x = extractFeature(text, featureMap);
              int y = featureMap.tagSet.add(label);
              if (y == 0)
                  y = -1; // 感知机标签约定为±1
              else if (y > 1)
                  throw new IllegalArgumentException("类别数大于2，目前只支持二分类。");
              instanceList.add(new Instance(x, y));
          }
          return instanceList.toArray(new Instance[0]);
      }
docs: 从语料库读取实例
  
  @param corpus     语料库
  @param featureMap 特征映射
  @return 数据集