nested array flatten and then group by - Apache drill

[yousuf]

Hi,

How can I retrieve hashtags[n].text values as flatten from the following 
json document (storage mongo). My final goal is to group text with count.

Apache drill version : 1.8.0
MongoDB version: 3.2

I've tried several examples but my final result is either empty array eg 
[] or blank.

{
    "twitter_entities": {
        "hashtags": [{
            "text": "snow",
            "indices": [
                66,
                71
            ]
        }, {
            "text": "skiing",
            "indices": [
                73,
                80
            ]
        }],
        "trends": [],
        "urls": [{
            "url": "http://xxxxxxx";,
            "expanded_url": "http://xxxxx";,
            "display_url": xxxxx",
            "indices": [
                71,
                93
            ]
        }]
    }
}

Any help is appreciated
Regards
Yousuf