random playing soundfiles according to rating.

[Michael Spencer]

kp87 at lycos.com wrote:
...

> 
> But i am stuck on how to do a random chooser that works according to my
> idea of choosing according to rating system. It seems to me to be a bit
> different that just choosing a weighted choice like so:
> 
...
> 
> And i am not sure i want to have to go through what will be hundreds of
> sound files and scale their ratings by hand so that they all add up to
> 100%. I just want to have a long list that i can add too whenever i
> want, and assign it a grade/rating according to my whims!
> 
Perhaps something like this:

from bisect import bisect_left
from random import randrange

def w_choice(range, weights):
     """Return a choice from range, given *cumulative* relative frequencies"""
     total = weights[-1]
     pick = randrange(1,total)
     ix = bisect_left(weights, pick)
     return range[ix]


def cum_sum(iterable, start = 0):
     cum = []
     for i in iterable:
         start += i
         cum.append(start)
     return cum

Test it:
  >>> files = {"File1": 20, "File2": 10, "File3":70}
  >>> def test(files, N = 10000):
  ...     names = files.keys()
  ...     weights = cum_sum(files.values())
  ...
  ...     plays = {}
  ...     for i in range(N):
  ...         track = w_choice(names, weights)
  ...         plays[track] = plays.get(track, 0) + 1
  ...     return plays
  ...
  >>> test(files, N=10000)
  {'File3': 7039, 'File2': 1049, 'File1': 1912}
  >>> files["File4"] = 50
  >>> test(files, N=150000)
  {'File3': 70502, 'File2': 9988, 'File1': 20009, 'File4': 49501}
  >>>


Michael