Database
[{"d":"a"},{"d":"b"}]
Query
db.collection.aggregate([{$replaceRoot:{newRoot:{"$mergeObjects":["$$ROOT",{"$arrayToObject":{$map:{input:{$filter:{input:{"$objectToArray":{"a":"qwerty1","b":"poiuy2p","c":"asdfg3"}},cond:{$eq:["$$this.k","$d"]}}},in:{k:"dummy",v:"$$this.v"}}}}]}}}])