code: @Override
      public Map<List<String>, String[]> getSimpleColumnsMaster(String[] masterLabels,
                                                                int[] joinColumnNo,
                                                                String path,
                                                                String separator)
                                                                    throws IOException, URISyntaxException {
          Map<List<String>, String[]> m = new HashMap<List<String>, String[]>();
  
          FileSystem fs = FileSystem.get(conf);
          FileStatus fstatus = fs.getFileStatus(new Path(path));
          if (fstatus == null) {
              return null;
          }
  
          BufferedReader br =
                  new BufferedReader(new InputStreamReader(fs.open(fstatus.getPath())));
  
          String line;
          while ((line = br.readLine()) != null) {
              String[] strings = StringUtil.split(line, separator, false);
              if (masterLabels.length != strings.length) {
                  continue;
              }
  
              List<String> joinData = new ArrayList<String>();
              for (int i : joinColumnNo) {
                  joinData.add(strings[i]);
              }
  
              String[] data = new String[strings.length];
              for (int i = 0; i < strings.length; i++) {
                  data[i] = strings[i];
              }
  
              m.put(joinData, data);
          }
          br.close();
  
          return m;
      }
docs: {@inheritDoc}