elsa wrote: > Hi guys, > > I've got a problem with my program, in that the code just takes too > long to run. Here's what I'm doing. If anyone has any tips, they'd be > much appreciated! > > So, say I have a list of lists that looks something like this (I'm > using a list of lists, rather than a list of tuples, as I need it to > be mutable): > > myList = [[786,0],[45, 1],[673,1],...................[23,46]] > > there are enough entries in the outer list, that the sum of myList[i] > [0] across all i could be as high as 10^7. > > Now, what I need to do is randomly choose one myList[i], however the > distribution of my random choice needs to be proportional to the > values of myList[i][0]. So, for this list above, I'd have a much > higher chance of choosing myList[0] than myList[1]. > > Here is how I'm doing it at the moment: > > def chooseI(myList): > mySum=0 > choice = random.choice(range(1,sum([i[0] for i in myList])+1)) > for i in range(len(myList)): > mySum+=myList[i][0] > if mySum>=choice: > return i > break > > This works just fine if sum([i[0] for i in myList]) is less than > 10,000, say. However if its up around 10^7, the whole thing crashes. > Is there a faster way of doing this, that doesn't involve as many > computational steps?
Do the first items of the inner lists change often? If not you can put the running sum into them, i. e. myList = [[768, ...], [786+45, ...], [786+45+673, ...], ...] and use bisect.bisect() to choose the item. Peter -- http://mail.python.org/mailman/listinfo/python-list
