elasticsearch-analysis-pinyin 1.7.4 怎么提取首字母

elasticsearch-analysis-pinyin 1.7.4 版本怎么提取首字母？好像只是提供了转化为拼音的功能。（线上跑的2.3.4版本的es，升级怕丢失数据）
 
附索引设置：
{
    "settings":{
        "analysis":{
            "analyzer":{
                "pinyin_analyzer":{
                    "tokenizer":"my_pinyin"
                }
            },
            "tokenizer":{
                "my_pinyin":{
                    "type":"pinyin",
                    "keep_separate_first_letter":true,
                    "keep_full_pinyin":true,
                    "keep_original":true,
                    "limit_first_letter_length":16,
                    "lowercase":true
                }
            }
        }
    },
    "mappings":{
        "user":{
            "properties":{
                "title":{
                    "type":"string",
                    "analyzer":"ik_max_word"
                },
                "user_pinyin_title":{
                    "type":"string",
                    "store":"yes",
                    "term_vector":"with_offsets",
                    "analyzer":"pinyin_analyzer"
                },
                "biography":{
                    "type":"string",
                    "analyzer":"ik_max_word"
                }
            }
        }
    }
}