Bruza wrote: > I need to implement a "random selection" algorithm which takes a list > of [(obj, prob),...] as input. Each of the (obj, prob) represents how > likely an object, "obj", should be selected based on its probability > of > "prob".To simplify the problem, assuming "prob" are integers, and the > sum of all "prob" equals 100. For example, > > items = [('Mary',30), ('John', 10), ('Tom', 45), ('Jane', 15)] > > The algorithm will take a number "N", and a [(obj, prob),...] list as > inputs, and randomly pick "N" objects based on the probabilities of > the > objects in the list. > > > For N=1 this is pretty simply; the following code is sufficient to do > the job. > > def foo(items): > index = random.randint(0, 99) > currentP = 0 > for (obj, p) in items: > currentP += w > if currentP > index: > return obj > > But how about the general case, for N > 1 and N < len(items)? Is there > some clever algorithm using Python standard "random" package to do > the trick? >
I think you need to clarify what you want to do. The "probs" are clearly not probabilities. Are they counts of items? Are you then sampling without replacement? When you say N < len(items) do you mean N <= sum of the "probs"? Duncabn -- http://mail.python.org/mailman/listinfo/python-list