itertools

问题 I know how to get ALL combinations of a list in Python with itertools, but what if I want to limit the amount of repeats? So, if I have [1, 2, 3, 4, 5] But I want to limit combinations to only 3 repeats of each item (with a fixed length of the final list, say 10): [1, 1, 1, 2, 3, 3, 5, 5, 5, 4] [1, 2, 3, 3, 3, 4, 5, 5, 4, 4] [4, 4, 1, 1, 1, 5, 2, 2, 2, 3] and so on. How do I do this? 回答1: This would work: import random L = [1, 2, 3, 4, 5] L3 = L * 3 random.shuffle(L3) L3[:10] 回答2: I don't

问题 This code: from itertools import groupby, count L = [38, 98, 110, 111, 112, 120, 121, 898] groups = groupby(L, key=lambda item, c=count():item-next(c)) tmp = [list(g) for k, g in groups] Takes [38, 98, 110, 111, 112, 120, 121, 898] , groups it by consecutive numbers and merge them with this final output: ['38', '98', '110,112', '120,121', '898'] How can the same be done with a list of lists with multiple columns, like this list below where you can group them by name and the consecution of its

问题 The recipe section of itertools docs begins with this text: The extended tools offer the same high performance as the underlying toolset. The superior memory performance is kept by processing elements one at a time rather than bringing the whole iterable into memory all at once. Code volume is kept small by linking the tools together in a functional style which helps eliminate temporary variables. High speed is retained by preferring “vectorized” building blocks over the use of for-loops and

问题 I am having performance issues with my code. step # IIII consumes hours of time. I used to materialize the the itertools.prodct before, but thanks to a user I dont do pro_data = product(array_b,array_a) anymore. This helped me with memory issues, but the still is heavily time consuming. I would like to paralellize it with multithreading or multiprocesisng, whatever you can suggest, I am grateful. Explanation. I have two arrays that contain x and y values of particles. For each particle

问题 I want to chunk an input stream for batch processing. Given an input list or generator, x_in = [1, 2, 3, 4, 5, 6 ...] I want a function that will return chunks of that input. Say, if chunk_size=4 , then, x_chunked = [[1, 2, 3, 4], [5, 6, ...], ...] This is something I do over and over, and was wondering if there is a more standard way than writing it myself. Am I missing something in itertools ? (One could solve the problem with enumerate and groupby , but that feels clunky.) In case anyone

问题 I am trying to write a module to combine a variable number of lists using itertools.product. The closest I can get is: import itertools lists = [["item1","item2"],["A","b","C"], ["etc..."]] searchterms = list(itertools.product(lists)) print searchterms This doesn't work, because lists is a single list, so it just returns the original sequence. But I can't figure out how to pass each element of the lists variable to itertools. Thanks for any suggestions. 回答1: You need to use * to separate the

问题 I am new at Python, trying to build an old python file into Python 3. I got several build errors which I solved. But at this point I am getting above error. I have no idea how to fix this. The code section looks like below. return itertools.ifilter(lambda i: i.state == "IS", self.storage) 回答1: itertools.ifilter() was removed in Python 3 because the built-in filter() function provides the same functionality now. If you need to write code that can run in both Python 2 and Python 3, use imports

问题 I have a list of servers. Every server has a list of name on it. example: server1 = ['a','b','c'] server2 = ['d','e','f'] server3 = ['g','h','i'] I want to iterate per server name not per server. For example after picking 'a' in server1 , move to 'd' (not 'b' ) and so on. If I'm going to use itertools.cycle() , do I have to create a list of server to cycle through? My expected result is ['a','d','g','b','e','h','c','f','i'] . Can you give me a simple example on how to cycle in multiple list.

问题 This question already has answers here : Flatten an irregular list of lists (44 answers) Closed 4 years ago . I've seen a couple answers on how to flatten lists of the form [1,[1,2],[3]] print list(itertools.chain(*[1,[1,2],[3]])) but how do you flatten lists like this: [[1],[[1,2],[3]]] print list(itertools.chain(*[[1],[[1,2],[3]]])) [1, [1, 2], [3]] 回答1: I usually use this recipe: import collections def flatten(l): for el in l: if isinstance(el, collections.Iterable) and not isinstance(el,

问题 I'm processing a huge number of combinations of items (from League of Legends), about 72 million, all of which are fed into a function that calculates how beneficial they are. We're trying to find the best possible combination. Ignoring the fact that there might be better ways, algorithmically speaking, to do this, can anyone tell me why I'm getting a memory error? allpossiblei = itertools.combinations(items.keys(),5) maxc = 0 i = 0 for combo in allpossiblei: icombo = [items[name] for name in