Database
[{"_id":{"SpId":250,"Channel_Id":2,"TweetId":1},"Sentiment":-0.83,"AgeGroup":"13-17","Gender":"F","Location":{"Country":"Russia","Lat":"46.7323875","Long":"-117.0001651","City":"Moscow"},"IdeaCloudText":" PS_realized PS_have PS_enough NG_drunk"},{"_id":{"SpId":250,"Channel_Id":2,"TweetId":2},"Sentiment":-0.70,"AgeGroup":"21-40","Gender":"F","Location":{"Country":"United States","Lat":"25.4791234","Long":"-142.0001651","City":"LA"},"IdeaCloudText":" PS_good NG_dangerous"}]
Query
db.collection.aggregate([{$match:{"_id.SpId":250}},{"$group":{"_id":{"SpId":"$_id.SpId","Channel_Id":"$_id.Channel_Id"},"IdeaCloudText":{"$addToSet":"$IdeaCloudText"}}},{"$addFields":{"IdeaCloudText":{"$reduce":{"input":"$IdeaCloudText","initialValue":"","in":{"$concat":["$$value","$$this"]}}}}}])