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A map-reduce that calculates the density for each
of a set of tracks. The track density is the average
number of segments per segment for a track.
from mrjob.job import MRJob
import track
# if YIELD_ALL is true, we yield all densities, otherwise,
# we yield just the extremes
class MRDensity(MRJob):
""" A map-reduce job that calculates the density """
def mapper(self, _, line):
""" The mapper loads a track and yields its density """
t = track.load_track(line)
if t:
if t['tempo'] > 0:
density = len(t['segments']) / t['duration']
#only output extreme density
if YIELD_ALL or density > 8 or density < .5:
yield (t['artist_name'], t['title'], t['song_id']), density
# no need for a reducer
#def reducer(self, key, val):
#yield (key, sum(val))
if __name__ == '__main__':