My attempts at MapReduce using MongoDB

I was sorting a tree in my (python) webapp instead of having the database to do it for me. This is how I moved it back to the database by using a MapReduce job. I had a collection structured like the following:

{
  "_id" : ...,
  "feed_oid" : "4fd268d2ab87b2d8927d7eee",
  "title" : "blah blah",
  "updated" : 1339702524,
  "watchers" : [ "4fd276fc66224c1ee8000006" ]
}

Such a collection is called articles and in there I get a document for every article published by an rss feed. feed_oid is …