gistfile1.js

map = function () {
    emit(this.id, this.version);
}

reduce = function (key, values) {
    return Math.max.apply(Math, values);
}

fin = function(key, value) {
  return db.oplan.findOne({id:key, version:value});
}

db.oplan.mapReduce(map,reduce, {out:'versions', finalize:fin});

function (key, values) {
return db.oplan.findOne({id:key, version:Math.max.apply(Math, values)});
}

db.oplan.mapReduce(map,reduce, {out:'res'});
{
"result" : "res",
"timeMillis" : 12,
"counts" : {
"input" : 3,
"emit" : 3,
"output" : 2
},
"ok" : 1,
}
db.res.find();
{ "_id" : "1234A", "value" : { "_id" : ObjectId("4bf80c47e65228196db0a382"), "id" : "1234A", "version" : 1 } }
{ "_id" : "1234T", "value" : null }