[source, ruby]
----
response = client.search(
  body: {
    size: 0,
    runtime_mappings: {
      normalized_genre: {
        type: 'keyword',
        script: "\n        String genre = doc['genre'].value;\n        if (doc['product'].value.startsWith('Anthology')) {\n          emit(genre + ' anthology');\n        } else {\n          emit(genre);\n        }\n      "
      }
    },
    aggregations: {
      genres: {
        terms: {
          field: 'normalized_genre'
        }
      }
    }
  }
)
puts response
----
