way_classifer.py

# -*- coding: utf-8 -*-
"""
Created on Sun Oct 12 17:25:10 2014

@author: vikramk3
"""

#!/usr/bin/env python
"""
Use an aggregation query to answer the following question.

Which Way, based on id, is one-way, closed, or an area?

In my analysis, if a way has two of the same nodes, it is closed. If it has all unique nodes, it
is one way. If the way has three of the same nodes, it is an area.

Please modify only the 'make_pipeline' function so that it creates and returns an aggregation
pipeline that can be passed to the MongoDB aggregate function. As in our examples in this lesson,
the aggregation pipeline should be a list of one or more dictionary objects.
Please review the lesson examples if you are unsure of the syntax.

This code was run locally on my machine and the data set is a smaller version of the
the complete Austin, TX OSM data set.

"""

def get_db(db_name):
    from pymongo import MongoClient
    client = MongoClient('localhost:27017')
    db = client[db_name]
    return db

def make_pipeline():
    # complete the aggregation pipeline
    pipeline = [{"$match":{"type":"way"}},{"$unwind":"$node_refs"},{"$group":{"_id":{"id":"$id", "node_refs":"$node_refs"}, "count":{"$sum":1}}}, {"$sort":{"count":-1}},{"$limit":100}]
    return pipeline

def aggregate(db, pipeline):
    result = db.cities.aggregate(pipeline)
    return result

if __name__ == '__main__':
    db = get_db('examples')
    pipeline = make_pipeline()
    result = aggregate(db, pipeline)
    #print result
    import pprint
    pprint.pprint(result)