Template
single collection
multiple collections
mgodatagen
update
indexe
explain
Stage
Database
bson
mgodatagen
[{_id:1,values:["1","2","4"]},{_id:2,values:["1","3","5"]}]
Query
db.collection.aggregate([{$project:{"values":{$reduce:{input:"$values",initialValue:[],in:{$concatArrays:["$$value","$$this"]}}}}}])
Result