@Override
	public String getFeature(int wordId, int... fields) {
		String[] allFeatures = getAllFeaturesArray(wordId);
		if (allFeatures == null) {
			return null;
		}
		StringBuilder sb = new StringBuilder();
		if (fields.length == 0) { // All features
			for (String feature : allFeatures) {
				sb.append(CSVUtil.quoteEscape(feature)).append(",");
			}
		} else if (fields.length == 1) { // One feature doesn't need to escape value
			sb.append(allFeatures[fields[0]]).append(",");
		} else {
			for (int field : fields){
				sb.append(CSVUtil.quoteEscape(allFeatures[field])).append(",");
			}
		}
		return sb.deleteCharAt(sb.length() - 1).toString();
	}