Mappingでdoubleを指定して、文字列で数値データ登録してみたらどうなるか。 ※0.90.7で実験

double_mapping_test.json

# index作成
curl -XPUT localhost:9200/hoge
# mappingの指定
curl -XPUT localhost:9200/hoge/fuga/_mapping -d '{
    "fuga" : {
        "numeric_detection" : false,
        "properties" : {
            "Resp_Time" : {"type" : "double"}
        }
    }
}'

# データ登録（文字列？）
curl -XPUT localhost:9200/hoge/fuga/1 -d '{"Resp_Time" : "12.09" }'
curl -XPUT localhost:9200/hoge/fuga/2 -d '{"Resp_Time" : "12.11" }'

# 検索実施（statistical facetを利用：数値or日付データしか計算出来ない。http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/search-facets-statistical-facet.html）
curl -XPOST "http://localhost:9200/fuga/fuga/_search?pretty" -d'
> {
>     "query" : {
>         "match_all": {}
>     },
>     "facets" : {
>         "stat1" : {
>             "statistical" : {
>                 "field" : "Resp_Time"
>             }
>         }
>     }
> }'

# 結果
{
  "took" : 5,
  "timed_out" : false,
  "_shards" : {
    "total" : 5,
    "successful" : 5,
    "failed" : 0
  },
  "hits" : {
    "total" : 2,
    "max_score" : 1.0,
    "hits" : [ {
      "_index" : "fuga",
      "_type" : "fuga",
      "_id" : "2",
      "_score" : 1.0, "_source" : {
"Resp_Time" : "12.11" }
    }, {
      "_index" : "fuga",
      "_type" : "fuga",
      "_id" : "1",
      "_score" : 1.0, "_source" : {
"Resp_Time" : "12.09" }
    } ]
  },
  "facets" : {
    "stat1" : {
      "_type" : "statistical",
      "count" : 2,
      "total" : 24.2,
      "min" : 12.09,
      "max" : 12.11,
      "mean" : 12.1,
      "sum_of_squares" : 292.8202,
      "variance" : 1.0000000000331966E-4,
      "std_deviation" : 0.010000000000165982
    }
  }
}