kibana上看到的字段都是字符串，如何针对性的修改为数值型

请教大家，由logstash吐到elasticsearch，然后通过kibana查看对应信息。计划生成基于某字段平均数的曲线图，但发现分解的所有字段都是字符串，如何调整。谢谢

其中logstash的配置：
input {
    redis {
            host => "172.23.11.100"
            port => 6379
                key => "filebeat"
                type => "filebeat"
                data_type => "list"
        }
}

filter {
    if [type] == "monitor_access_log" {
      grok {
        match => { "message" => "%{TIMESTAMP_ISO8601:timestamp}\|%{LOGLEVEL:level}\|%{WORD:filename}\|%{WORD:method}\|%{URIPATHPARAM:request}\|(?:HTTP/%{NUMBER:http_version})\|%{IP:client}\|%{INT:http_status_code}\|%{NUMBER:duration}\|(?<reserve1>([\s\S]*))\|(?<reserve2>([\s\S]*))\|(?<reserve3>([\s\S]*))"
            }
        }
    }
}

output {
        if [type] == "monitor_access_log" {
                elasticsearch {
                        hosts => ["172.23.11.136:9200","172.23.11.137:9200","172.23.11.138:9200"]
                        index => "omp-monitor-access-%{+YYYY.MM.dd}"
                }
                stdout {
                                        codec => rubydebug
                }
        }
}