Re: Weighted random selection from list of lists
On Sat, 08 Oct 2005 12:48:26 -0400, Jesse Noller wrote: Once main_list is populated, I want to build a sequence from items within the lists, randomly with a defined percentage of the sequence coming for the various lists. For example, if I want a 6 item sequence, I might want: 60% from list 1 (main_list[0]) 30% from list 2 (main_list[1]) 10% from list 3 (main_list[2]) If you are happy enough to match the percentages statistically rather than exactly, simply do something like this: pr = random.random() if pr 0.6: list_num = 0 elif pr 0.9: list_num = 1 else: list_num = 2 return random.choice(main_list[list_num]) or however you want to extract an item. On average, this will mean 60% of the items will come from list1 etc, but for small numbers of trials, you may have significant differences. -- Steven. -- http://mail.python.org/mailman/listinfo/python-list
Re: Weighted random selection from list of lists
Jesse Noller wrote: 60% from list 1 (main_list[0]) 30% from list 2 (main_list[1]) 10% from list 3 (main_list[2]) I know how to pull a random sequence (using random()) from the lists, but I'm not sure how to pick it with the desired percentages. Any help is appreciated, thanks -jesse Just add up the total of all lists. total = len(list1)+len(list2)+len(list3) n1 = .60 * total# number from list 1 n2 = .30 * total# number from list 2 n3 = .10 * total# number from list 3 You'll need to decide how to handle when a list has too few items in it. Cheers, Ron -- http://mail.python.org/mailman/listinfo/python-list
Re: Weighted random selection from list of lists
Jesse Noller wrote: I'm probably missing something here, but I have a problem where I am populating a list of lists like this: list1 = [ 'a', 'b', 'c' ] list2 = [ 'dog', 'cat', 'panda' ] list3 = [ 'blue', 'red', 'green' ] main_list = [ list1, list2, list3 ] Once main_list is populated, I want to build a sequence from items within the lists, randomly with a defined percentage of the sequence coming for the various lists. For example, if I want a 6 item sequence, I might want: 60% from list 1 (main_list[0]) 30% from list 2 (main_list[1]) 10% from list 3 (main_list[2]) I know how to pull a random sequence (using random()) from the lists, but I'm not sure how to pick it with the desired percentages. If the percentages can be normalized to small integral numbers, just make a pool where each list is repeated according to its weight, e. g. list1 occurs 6, list2 3 times, and list3 once: pools = [list1, list2, list3] weights = [6, 3, 1] sample_size = 10 weighted_pools = [] for p, w in zip(pools, weights): weighted_pools.extend([p]*w) sample = [random.choice(random.choice(weighted_pools)) for _ in xrange(sample_size)] Another option is to use bisect() to choose a pool: pools = [list1, list2, list3] sample_size = 10 def isum(items, sigma=0.0): for item in items: sigma += item yield sigma cumulated_weights = list(isum([60, 30, 10], 0)) sigma = cumulated_weights[-1] sample = [] for _ in xrange(sample_size): pool = pools[bisect.bisect(cumulated_weights, random.random()*sigma)] sample.append(random.choice(pool)) (all code untested) Peter -- http://mail.python.org/mailman/listinfo/python-list
Re: Weighted random selection from list of lists
Jesse Noller wrote: paraphrased Once main_list is populated, I want to build a sequence from items within the lists, randomly with a defined percentage of the sequence coming for the various lists. For example: 60% from list 1 (main_list[0]), 30% from list 2 (main_list[1]), 10% from list 3 (main_list[2]) import bisect, random main_list = [['a', 'b', 'c'], ['dog', 'cat', 'panda'], ['blue', 'red', 'green']] weights = [60, 30, 10] cumulative = [] total = 0 for index, value in enumerate(weights): total += value cumulative.append(total) for i in range(20): score = random.random() * total index = bisect.bisect(cumulative, score) print random.choice(main_list[index]), -- -Scott David Daniels [EMAIL PROTECTED] -- http://mail.python.org/mailman/listinfo/python-list
