[{"rule_id":"rule_1","description":"desc_rule_1_version_1","version":1},{"rule_id":"rule_1","description":"desc_rule_1_version_2","version":2},{"rule_id":"rule_2","description":"desc_rule_2_version_1","version":1}]

db.collection.aggregate([{"$group":{"_id":"$rule_id","docs":{"$push":"$$ROOT"},"latestVersion":{"$max":"$version"}}},{"$project":{"latest":{"$first":{"$filter":{"input":"$docs","as":"doc","cond":{"$eq":["$$doc.version","$latestVersion"]}}}}}},{"$replaceWith":"$latest"}])