How to sort ordinal values in elasticsearch? - elasticsearch

Question

Say i've got a field 'spicey' with possible values 'hot', 'hotter', 'smoking'.
There's an intrinsic ordening in these values: they're ordinals.
I'd like to be able to sort or filter on them using their intrinsic order. For example: give me all documents where spicey > hot.
Sure i can translate the values to integers 0,1,2 but this requires extra housekeeping on both the index and the query side which I'd rather avoid.
Is this possible in some way? Already contemplated using multi field mapping but not sure if that would help me.

Answer 1

You can sort based on string values by scripting a sort operation, so that you set each spicey string a specific field value.
curl -XGET 'http://localhost:9200/yourindex/yourtype/_search' -d
{
"sort": {
"_script": {
"script": "factor.get(doc[\"spicey\"].value)",
"type": "number",
"params": {
"factor": {
"hot": 0,
"hotter": 1,
"smoking": 2
}
},
"order": "asc"
}
}
}

Answer 2

One solution could be to create a specific analyzer for spice levels. The idea is to map each level to a discrete value which increases the more spicy the spice is.
{
"settings": {
"analysis": {
"char_filter": {
"spices": {
"type": "mapping",
"mappings": [
"mild=>1",
"hot=>2",
"hotter=>3",
"smoking=>4"
]
}
},
"analyzer": {
"spice_synonyms": {
"type": "custom",
"char_filter": "spices",
"tokenizer": "standard",
"filter": [
"standard"
]
}
}
}
},
"mappings": {
"ordinal": {
"properties": {
"spicy": {
"type": "string",
"fields": {
"level": {
"type": "string",
"analyzer": "spice_synonyms"
}
}
}
}
}
}
}
In the above index settings and mappings, the spicy field would contain the plain english word (hot, mild, etc) while the spicy.level field would contain a discrete value that you can then use in queries and sorting.
For instance, retrieving documents whose spice level is strictly bigger than hot and ordered in decreasing order (smoking first) could be done like this:
{
"sort": {
"spicy.level": "desc"
},
"query": {
"query_string": {
"query": "spicy.level:>2"
}
}
}
or a range query would work, too
{
"sort": {
"spicy.level": "desc"
},
"query": {
"range": {
"spicy.level" {
"gt": 2
}
}
}
}