Calculate 2010 batting wOBA

wOBA.py

from bson.code import Code

import pymongo


connection = pymongo.connection.Connection()
db = connection['retrosheet']
tbl = db['events_2010']

# limit results to complete plate appearances.
filters = {'PA_NEW_FL': 'T', 'PA_TRUNC_FL': 'F'}

# map all plate appearances
map_f = """
function() {
    var woba_fields = {nibb: (this.EVENT_CD == '14') ? 1 : 0, 
                       hbp: (this.EVENT_CD == '15') ? 1 : 0, 
                       _1b: (this.EVENT_CD == '20') ? 1 : 0, 
                       _2b: (this.EVENT_CD == '21') ? 1 : 0, 
                       _3b: (this.EVENT_CD == '22') ? 1 : 0, 
                       hr: (this.EVENT_CD == '23') ? 1 : 0, 
                       rboe: (this.BAT_SAFE_ERR_FL == 'T') ? 1 : 0,
                       pa: 1};
    emit(this.BAT_ID, woba_fields);
}
"""

# tally wOBA components
reduce_f = """
function(key, values) {
    var result = {nibb: 0, hbp: 0, _1b: 0, _2b: 0, _3b: 0, hr: 0, rboe: 0, pa: 0};

    for(var i in values) {
        result.nibb += values[i].nibb;
        result.hbp += values[i].hbp;
        result._1b += values[i]._1b;
        result._2b += values[i]._2b;
        result._3b += values[i]._3b;
        result.hr += values[i].hr;
        result.rboe += values[i].rboe;
        result.pa += values[i].pa;
    }

    return result;
}
"""

# calculate wOBA
finalize_f = """
function(key, result) {
    return ((0.72 * result.nibb) + (0.75 * result.hbp) + (0.9 * result._1b) + (0.92 * result.rboe) + 
            (1.24 * result._2b) + (1.56 * result._3b) + (1.95 * result.hr)) / result.pa;
}
"""

# run wOBA map/reduce job, persisting results in a collection called "woba_2010".
results = tbl.map_reduce(Code(map_f), Code(reduce_f), 'woba_2010', 
                         query=filters, 
                         finalize=Code(finalize_f))

for result in results.find():
    print result