[{id:1,number:10},{id:2,number:11},{id:3,number:12}]

db.collection.aggregate([{"$lookup":{"from":"collection","let":{"number":"$number"},pipeline:[{$match:{$expr:{$ne:["$number","$$number"]}}}],"as":"other_numbers"}},{"$set":{"other_numbers":"$other_numbers.number"}}])