Database
[{"filename":"anomaly-detection-using-amazon.pdf","tags":[{"entity":"Aws","count":21},{"entity":"Keras","count":1},{"entity":"Amazon Ml","count":1},{"entity":"Amazon Cloudwatch","count":1}]}]
Query
db.collection.aggregate([{$set:{tags:{$filter:{input:"$tags",cond:{$gt:[{$strLenCP:"$$this.entity"},3]}}}}}])