我需要一个滚动窗口(又名滑动窗口)可迭代的序列/迭代器/生成器。(默认的Python迭代可以被认为是一种特殊情况，其中窗口长度为1。)我目前正在使用以下代码。我怎样才能做得更优雅和/或更有效?
def rolling_window(seq, window_size):
it = iter(seq)
win = [it.next() for cnt in xrange(window_size)] # First window
yield win
for e in it: # Subsequent windows
win[:-1] = win[1:]
win[-1] = e
yield win
if __name__=="__main__":
for w in rolling_window(xrange(6), 3):
print w
"""Example output:
[0, 1, 2]
[1, 2, 3]
[2, 3, 4]
[3, 4, 5]
"""
对于window_size == 2的特定情况(即，在序列中迭代相邻的重叠对)，请参见如何从列表中迭代重叠(当前，下一个)值对?
为什么不
def pairwise(iterable):
"s -> (s0,s1), (s1,s2), (s2, s3), ..."
a, b = tee(iterable)
next(b, None)
return zip(a, b)
它被记录在Python文档中。
您可以轻松地将其扩展到更宽的窗口。
有一个库可以完全满足你的需要:
import more_itertools
list(more_itertools.windowed([1,2,3,4,5,6,7,8,9,10,11,12,13,14,15],n=3, step=3))
Out: [(1, 2, 3), (4, 5, 6), (7, 8, 9), (10, 11, 12), (13, 14, 15)]
在旧版本的Python文档中有一个itertools示例:
from itertools import islice
def window(seq, n=2):
"Returns a sliding window (of width n) over data from the iterable"
" s -> (s0,s1,...s[n-1]), (s1,s2,...,sn), ... "
it = iter(seq)
result = tuple(islice(it, n))
if len(result) == n:
yield result
for elem in it:
result = result[1:] + (elem,)
yield result
文档中的那个更简洁一点，我想它使用了itertools来达到更好的效果。
如果你的迭代器是一个简单的列表/元组，用指定的窗口大小滑动它的简单方法是:
seq = [0, 1, 2, 3, 4, 5]
window_size = 3
for i in range(len(seq) - window_size + 1):
print(seq[i: i + window_size])
输出:
[0, 1, 2]
[1, 2, 3]
[2, 3, 4]
[3, 4, 5]
deque窗口的一个轻微修改版本，使其成为一个真正的滚动窗口。因此，它开始只填充一个元素，然后增长到它的最大窗口大小，然后缩小，因为它的左边缘接近结束:
from collections import deque
def window(seq, n=2):
it = iter(seq)
win = deque((next(it, None) for _ in xrange(1)), maxlen=n)
yield win
append = win.append
for e in it:
append(e)
yield win
for _ in xrange(len(win)-1):
win.popleft()
yield win
for wnd in window(range(5), n=3):
print(list(wnd))
这给了
[0]
[0, 1]
[0, 1, 2]
[1, 2, 3]
[2, 3, 4]
[3, 4]
[4]
让我们让它变懒!
from itertools import islice, tee
def window(iterable, size):
iterators = tee(iterable, size)
iterators = [islice(iterator, i, None) for i, iterator in enumerate(iterators)]
yield from zip(*iterators)
list(window(range(5), 3))
# [(0, 1, 2), (1, 2, 3), (2, 3, 4)]
toolz/cytoolz包有一个sliding_window函数。
>>> from cytoolz import sliding_window
>>> list(sliding_window(3, range(6))) # returns [(0, 1, 2), (1, 2, 3), (2, 3, 4), (3, 4, 5)]
