[{"_id":"0x026EFF","Stations":{"MP":false,"AS":true,"RW":true,"FT":true}},{"_id":"0x026F00","Stations":{"MP":null,"AS":true,"RW":true,"FT":false}},{"_id":"0x026F01","Stations":{"MP":null,"AS":true,"RW":false,"FT":null}},{"_id":"0x026F02","Stations":{"MP":null,"AS":null,"RW":true,"FT":false}},{"_id":"0x026F03","Stations":{"MP":null,"AS":true,"RW":null,"FT":false}}]

db.collection.aggregate([{$set:{Stations:{$objectToArray:"$Stations"}}},{$unwind:"$Stations"},{$group:{_id:"$Stations.k",count:{$sum:{$cond:{if:{$eq:["$Stations.v",true]},then:1,else:0}}}}},{$group:{_id:null,data:{$push:"$$ROOT"}}},{$replaceWith:{$arrayToObject:{$map:{input:"$data",in:{k:"$$this._id",v:"$$this.count"}}}}}])