random playing soundfiles according to rating.

[Steve Holden]

kp87 at lycos.com wrote:
> I am a little bit stuck ....
> 
> I want to play a bunch of soundfiles randomly, but i want to give each
> soundfile a rating (say 0-100) and have the likelihood that the file be
> chosen be tied to its rating so that the higher the rating the more
> likely a file is to be chosen.  Then i need some additional flags for
> repetition, and some other business. I am guessing a dictionary would
> be a great way to do this, with the key being the soundfile name and
> the values being my ratings and other flags & associated data.
> 
> #soundfile name : [rating, %chance it will repeat/loop]
> sfiles = { ("sf001") : [85, 15],
>      ("sf002") : [25, 75],
>      ("sf003") : [95, 45],
>      ("sf004") : [35, 95] }
> 
> 
> 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:
> 
> def windex(lst):
> 	'''an attempt to make a random.choose() function that makes weighted
> choices
> 
> 	accepts a list of tuples with the item and probability as a pair
> 	like: >>> x = [('one', 0.25), ('two', 0.25), ('three', 0.5)]
> 	>>> y=windex(x)'''
> 	n = random.uniform(0, 1)
> 	for item, weight in lst:
> 		if n < weight:
> 			break
> 		n = n - weight
> 	return item
> 
> 
> 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!
> 

A really cheesy scheme: decide you will allocate each file a probability 
between 0 and 10 or 1 and 10 - whatever. 100 may be a bit much - do you 
really need such fine discrimination?

If you have your list [(filename, prob), (filename, prob), ... ] then 
construct a filename list as follows:

flist = []
for filename, prob in lst:
     flist += [filename] * prob

Then choosing a filename becomes quite simple:

file_to_play = random.choice(flist)

The rest is up to you ...

regards
  Steve
-- 
Steve Holden       +44 150 684 7255  +1 800 494 3119
Holden Web LLC                     www.holdenweb.com
PyCon TX 2006                  www.python.org/pycon/