add a facet function to pick one result's value

The facet functions and analytics working great, especially with json API !

As a developer, I would like a facet function to get a field value from one record from a group, please see this facet query:

{
"schema": {
"slide_id":

{ "type": "long" }

,
"slide_name":

{ "type": "string" }

,
"slide_create_time":

{ "type": "timestamp" }

},

"facet.query": {
"slide_viewed": {
"type": "terms",
"field": "slide_id",
"facet": {
"avg_viewed_time": "avg(slide_viewed_time)",
"created_time": "max(slide_create_time)",
"slide_name": "ANY_FIRST_LAST_OR_FILTER(slide_name)"
}
},
"total": {
"type": "query",
"q": ":",
"facet":

{ "slide_num": "unique(slide_id)" }

}
}
}

when grouping by slide_id, I would love to have the a function that can pick a slide name from each group of slides with the same slide_id.

I know I can get the name by using sub facet, but it will be in one level deep, and I can't sort by it, it would be great to be in one flat level, so they can be sorted.

thanks!