Database

[{"title":"lenovo x-100","brand":"lenovo","category":"laptops","variant":[{"price":30000,"RAM":"4GB","storage":"256GB","screen":"full hd","chip":"i3"},{"price":35000,"RAM":"8GB","storage":"512GB","screen":"full hd","chip":"i5"},{"price":40000,"RAM":"12GB","storage":"2TB","screen":"uhd","chip":"i7"}],"salesCount":32,"buysCount":35,"viewsCount":60},{"title":"samsung12","brand":"lenovo","category":"mobile phones","variant":[{"price":11000,"RAM":"4GB","ROM":"32GB"},{"price":16000,"RAM":"6GB","ROM":"64GB"},{"price":21000,"RAM":"8GB","ROM":"128GB"}],"salesCount":48,"buysCount":39,"viewsCount":74}]

Query

db.collection.aggregate([{$match:{brand:"lenovo"}},{$group:{_id:"$brand",prices:{$push:"$variant.price"}}},{$project:{_id:1,minPrice:{$min:{"$reduce":{"input":"$prices","initialValue":[],"in":{"$concatArrays":["$$value","$$this"]}}}}}}])

Result