[{"username":"joy","size_info":[{"data1":"apple bear cat","data2":100},{"data1":"","data2":100},{"data1":"hug ill jump","data2":100}]}]

db.collection.update({},[{$set:{size_info:{$map:{input:"$size_info",in:{$mergeObjects:["$$this",{data3:{$first:{$getField:{field:"captures",input:{$regexFind:{input:"$$this.data1",regex:"^([^\\s]* [^\\s]*).*$"}}}}}}]}}}}}])