如何将任意长度的列表拆分为大小相等的块?


请参阅如果数据结果将直接用于循环,并且不需要存储,则如何以块形式遍历列表。

对于字符串输入的同一问题,请参见每n个字符拆分字符串?。相同的技术通常适用,但也有一些变化。


当前回答

这适用于v2/v3,可内联,基于生成器,仅使用标准库:

import itertools
def split_groups(iter_in, group_size):
    return ((x for _, x in item) for _, item in itertools.groupby(enumerate(iter_in), key=lambda x: x[0] // group_size))

其他回答

使用列表综合:

l = [1,2,3,4,5,6,7,8,9,10,11,12]
k = 5 #chunk size
print [tuple(l[x:y]) for (x, y) in [(x, x+k) for x in range(0, len(l), k)]]

我不喜欢按块大小拆分元素的想法,例如,脚本可以将101到3个块划分为[50,50,1]。为了我的需要,我需要按比例分配,保持秩序不变。首先我写了自己的剧本,效果很好,而且很简单。但我后来看到了这个答案,剧本比我的好,我想是这样的。这是我的脚本:

def proportional_dividing(N, n):
    """
    N - length of array (bigger number)
    n - number of chunks (smaller number)
    output - arr, containing N numbers, diveded roundly to n chunks
    """
    arr = []
    if N == 0:
        return arr
    elif n == 0:
        arr.append(N)
        return arr
    r = N // n
    for i in range(n-1):
        arr.append(r)
    arr.append(N-r*(n-1))

    last_n = arr[-1]
    # last number always will be r <= last_n < 2*r
    # when last_n == r it's ok, but when last_n > r ...
    if last_n > r:
        # ... and if difference too big (bigger than 1), then
        if abs(r-last_n) > 1:
            #[2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 7] # N=29, n=12
            # we need to give unnecessary numbers to first elements back
            diff = last_n - r
            for k in range(diff):
                arr[k] += 1
            arr[-1] = r
            # and we receive [3, 3, 3, 3, 3, 2, 2, 2, 2, 2, 2, 2]
    return arr

def split_items(items, chunks):
    arr = proportional_dividing(len(items), chunks)
    splitted = []
    for chunk_size in arr:
        splitted.append(items[:chunk_size])
        items = items[chunk_size:]
    print(splitted)
    return splitted

items = [1,2,3,4,5,6,7,8,9,10,11]
chunks = 3
split_items(items, chunks)
split_items(['a','b','c','d','e','f','g','h','i','g','k','l', 'm'], 3)
split_items(['a','b','c','d','e','f','g','h','i','g','k','l', 'm', 'n'], 3)
split_items(range(100), 4)
split_items(range(99), 4)
split_items(range(101), 4)

和输出:

[[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11]]
[['a', 'b', 'c', 'd'], ['e', 'f', 'g', 'h'], ['i', 'g', 'k', 'l', 'm']]
[['a', 'b', 'c', 'd', 'e'], ['f', 'g', 'h', 'i', 'g'], ['k', 'l', 'm', 'n']]
[range(0, 25), range(25, 50), range(50, 75), range(75, 100)]
[range(0, 25), range(25, 50), range(50, 75), range(75, 99)]
[range(0, 25), range(25, 50), range(50, 75), range(75, 101)]

不调用len(),这对大型列表很有用:

def splitter(l, n):
    i = 0
    chunk = l[:n]
    while chunk:
        yield chunk
        i += n
        chunk = l[i:i+n]

这是可迭代的:

def isplitter(l, n):
    l = iter(l)
    chunk = list(islice(l, n))
    while chunk:
        yield chunk
        chunk = list(islice(l, n))

上述产品的功能风味:

def isplitter2(l, n):
    return takewhile(bool,
                     (tuple(islice(start, n))
                            for start in repeat(iter(l))))

OR:

def chunks_gen_sentinel(n, seq):
    continuous_slices = imap(islice, repeat(iter(seq)), repeat(0), repeat(n))
    return iter(imap(tuple, continuous_slices).next,())

OR:

def chunks_gen_filter(n, seq):
    continuous_slices = imap(islice, repeat(iter(seq)), repeat(0), repeat(n))
    return takewhile(bool,imap(tuple, continuous_slices))

根据这个答案,得票最多的答案在最后留下一个“矮子”。这是我的解决方案,可以在没有矮子的情况下,尽可能地获得大小均匀的块。它基本上试图准确选择应该拆分列表的小数点,但只需将其舍入到最接近的整数:

from __future__ import division  # not needed in Python 3
def n_even_chunks(l, n):
    """Yield n as even chunks as possible from l."""
    last = 0
    for i in range(1, n+1):
        cur = int(round(i * (len(l) / n)))
        yield l[last:cur]
        last = cur

演示:

>>> pprint.pprint(list(n_even_chunks(list(range(100)), 9)))
[[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10],
 [11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21],
 [22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32],
 [33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43],
 [44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55],
 [56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66],
 [67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77],
 [78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88],
 [89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99]]
>>> pprint.pprint(list(n_even_chunks(list(range(100)), 11)))
[[0, 1, 2, 3, 4, 5, 6, 7, 8],
 [9, 10, 11, 12, 13, 14, 15, 16, 17],
 [18, 19, 20, 21, 22, 23, 24, 25, 26],
 [27, 28, 29, 30, 31, 32, 33, 34, 35],
 [36, 37, 38, 39, 40, 41, 42, 43, 44],
 [45, 46, 47, 48, 49, 50, 51, 52, 53, 54],
 [55, 56, 57, 58, 59, 60, 61, 62, 63],
 [64, 65, 66, 67, 68, 69, 70, 71, 72],
 [73, 74, 75, 76, 77, 78, 79, 80, 81],
 [82, 83, 84, 85, 86, 87, 88, 89, 90],
 [91, 92, 93, 94, 95, 96, 97, 98, 99]]

与排名前几的答案进行比较:

>>> pprint.pprint(list(chunks(list(range(100)), 100//9)))
[[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10],
 [11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21],
 [22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32],
 [33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43],
 [44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54],
 [55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65],
 [66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76],
 [77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87],
 [88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98],
 [99]]
>>> pprint.pprint(list(chunks(list(range(100)), 100//11)))
[[0, 1, 2, 3, 4, 5, 6, 7, 8],
 [9, 10, 11, 12, 13, 14, 15, 16, 17],
 [18, 19, 20, 21, 22, 23, 24, 25, 26],
 [27, 28, 29, 30, 31, 32, 33, 34, 35],
 [36, 37, 38, 39, 40, 41, 42, 43, 44],
 [45, 46, 47, 48, 49, 50, 51, 52, 53],
 [54, 55, 56, 57, 58, 59, 60, 61, 62],
 [63, 64, 65, 66, 67, 68, 69, 70, 71],
 [72, 73, 74, 75, 76, 77, 78, 79, 80],
 [81, 82, 83, 84, 85, 86, 87, 88, 89],
 [90, 91, 92, 93, 94, 95, 96, 97, 98],
 [99]]

上面的答案(由koffein给出)有一个小问题:列表总是被分割成相等数量的分割,而不是每个分区的项目数相等。这是我的版本。“//chs+1”考虑到项目的数量可能不能完全除以分区大小,因此最后一个分区将仅被部分填充。

# Given 'l' is your list

chs = 12 # Your chunksize
partitioned = [ l[i*chs:(i*chs)+chs] for i in range((len(l) // chs)+1) ]