simple ordering implementation in Python for foursquare hackathon dish ranking app - messy messy messy!

gistfile1.py

import json

TESTSTRING = '[{ "_id" : "HZXXY3", "venues" : { "A" : [ "B" ], "B" : [ "C" ], "C" : [ ] } }, { "_id" : "HZXXY4", "venues" : { "A" : [ "B" ], "B" : [ "C" ], "C" : [ ] } }, { "_id" : "HZXXY5", "venues" : { "A" : [ "B", "C"], "B" : [ "A", "C" ], "C" : ["A"] } }]'

# initialize ballot dict

# loop through records
# loop through venues
# add or increment "for" ballot for venue
# loop through beaten venues
# add or increment "against" ballot for venue

def increment_venue_ballot(v, k, ballot):
    """Given a venue id, 'for' or 'against' key, and the ballot 
       dictionary, increment the appropriate ballot field. 

       Ex.: 
         increment_venue_ballot('a', 'for', {})
         => {'a': {'against': 0, 'for': 1}}"""
    if not v in ballot:
        ballot[v] = {"for": 0, "against": 0}
    ballot[v][k] += 1
    return ballot

def parse_venue(rec, ballot):
    """Given record and ballot dictionaries, determine winner and loser."""
    for winner in rec["venues"].keys():
        if len(rec["venues"][winner]) > 0:
            ballot = increment_venue_ballot(winner, "for", ballot)
            for loser in rec["venues"][winner]:
                ballot = increment_venue_ballot(loser, "against", ballot)
    return ballot

def parse_records(recs):
    """Parse venues from user records, returning ballot"""
    ballot = dict()

    for rec in recs:
        ballot = parse_venue(rec, ballot)
    
    return ballot

def get_margin(votes):
    """Calculate voting margin (for - against)."""
    return votes["for"] - votes["against"]

def get_venue_tallies(ballot):
    """Tally up ballot for ranking."""
    tally = list()

    for venue in ballot.keys():
        tally.append({"venue":venue, 
                      "margin":get_margin(ballot[venue]),
                      "against":ballot[venue]["against"]})
    return tally

def rank_venues(tallies):
    """Rank venues based on vote margin and number of votes against
       (tiebreaker)."""
    sorted_tallies = sorted(tallies, 
                            key=lambda k: (-k['margin'], k['against']))
    return sorted_tallies

def main(s):
    records = json.loads(s)
    ballot = parse_records(records)
    tallies = get_venue_tallies(ballot)
    ranks = rank_venues(tallies)

    for rec in ranks:
        print rec["venue"], rec["margin"], rec["against"]

    return