public void LoadChildDirectory(String folder, String suffix) {
		if(folder==null||folder.isEmpty())
			return;
		
		int current = m_corpus.getSize();
		File dir = new File(folder);
		for(File f: dir.listFiles()){
			if(f.isFile() && f.getName().endsWith(suffix)){
				loadChildDoc(f.getAbsolutePath());
			}else if(f.isDirectory()){
				LoadChildDirectory(folder, suffix);
			}
		}
		System.out.format("loading %d comments from %s\n", m_corpus.getSize() - current, folder);

		filterParentAndChildDoc();
	}