Python列表组

Question

我有一个像这样的python列表：

Category    Title   ProductId   Rating
'Electronics, Books, Bundles'   Lautner e-Reader Cover  161553  4
'Electronics, Books, Bundles'   Lautner stand in e-Reader Cover 161552  3
'Electronics, Books, Bundles'   Lautner Chocolate NOOK Case 594451  5
'Electronics, Books, Bundles'   Oliver e-Reader Cover   161685  1
'Electronics, Books, Covers'    Dessin Leather Cover for Nook Color; Nook Tablet Digital Reader 594033  4.3
'Electronics, Books, Covers'    Emerson Quote e-Reader Cover    161542  2.8
'Electronics, Books, Covers'    Industriell Easel e-Reader Cover    161682  3.7
'Electronics, Books, Covers'    Jonathan Adler Book Reader Cover Hd - Elephant  594548  4.9
'Electronics, Scanners, Covers' Lyra Light Front Cover for NOOK eR  161683  4
'Electronics, Scanners, Covers' Nook Tablet Dessin Cover in Marine  161686  3.8
'Electronics, Scanners, Covers' Nook Tablet Horizontal Stand Cover in Red   594202  4.2
'Electronics, Scanners, Covers' Canvas Bella Library Cover  161554  3
'Electronics, Books, Radios'    Groovy Protective Stand Cover: Custom Designed for 7-inch NOOK HD   594549  3.8
'Electronics, Books, Radios'    Hd Groovy Stand In Blue- Nook   594514  4.1
'Electronics, Books, Radios'    Hutton Envelope in Bark 161560  2.9
'Electronics, Books, Radios'    Italian Leather-Style Chesterton Cover for NOOK Reader  161561  4

在所有这些列表值中，我想要每个类别中的顶部k。前2名应提供以下结果：

'Electronics, Books, Bundles'   Lautner Chocolate NOOK Case 594451  5
'Electronics, Books, Bundles'   Lautner e-Reader Cover  161553  4
'Electronics, Books, Covers'    Jonathan Adler Book Reader Cover Hd - Elephant  594548  4.9
'Electronics, Books, Covers'    Dessin Leather Cover for Nook Color; Nook Tablet Digital Reader 594033  4.3
'Electronics, Books, Radios'    Hd Groovy Stand In Blue- Nook   594514  4.1
'Electronics, Books, Radios'    Italian Leather-Style Chesterton Cover for NOOK Reader  161561  4
'Electronics, Scanners, Covers' Nook Tablet Horizontal Stand Cover in Red   594202  4.2
'Electronics, Scanners, Covers' Lyra Light Front Cover for NOOK eR  161683  4

添加我尝试过的东西：

sorted_data = sorted(data, key=operator.itemgetter(1), reverse=True)

k = int(sys.argv[1])
for result in sorted_data[:k]:
    print result

这里，我将'k‘作为命令行参数传递给python文件。

Answer 1

使用迭代器等，您可以获得相对高效的性能。注意:这使用了标准的Python库。

import heapq
import itertools

# group by 'Category'
groups = itertools.groupby(some_list, key=lambda element: element[0])

# take top two of each group based on 'Rating'
top_two_of_each = (heapq.nlargest(2, values, key=lambda value: value[3]) for 
_, values in groups)

# flatten the nested iterators
top_two_of_each_flattened = itertools.chain(*top_two_of_each)

# convert iterator into a list
top_two_of_each_flattened_as_list = list(top_two_of_each_flattened)

Answer 2

这可能是你所需要的：

data = ''''Electronics, Books, Bundles'   Lautner e-Reader Cover  161553  4
'Electronics, Books, Bundles'   Lautner stand in e-Reader Cover 161552  3
'Electronics, Books, Bundles'   Lautner Chocolate NOOK Case 594451  5
'Electronics, Books, Bundles'   Oliver e-Reader Cover   161685  1
'Electronics, Books, Covers'    Dessin Leather Cover for Nook Color; Nook Tablet Digital Reader 594033  4.3
'Electronics, Books, Covers'    Emerson Quote e-Reader Cover    161542  2.8
'Electronics, Books, Covers'    Industriell Easel e-Reader Cover    161682  3.7
'Electronics, Books, Covers'    Jonathan Adler Book Reader Cover Hd - Elephant  594548  4.9
'Electronics, Scanners, Covers' Lyra Light Front Cover for NOOK eR  161683  4
'Electronics, Scanners, Covers' Nook Tablet Dessin Cover in Marine  161686  3.8
'Electronics, Scanners, Covers' Nook Tablet Horizontal Stand Cover in Red   594202  4.2
'Electronics, Scanners, Covers' Canvas Bella Library Cover  161554  3
'Electronics, Books, Radios'    Groovy Protective Stand Cover: Custom Designed for 7-inch NOOK HD   594549  3.8
'Electronics, Books, Radios'    Hd Groovy Stand In Blue- Nook   594514  4.1
'Electronics, Books, Radios'    Hutton Envelope in Bark 161560  2.9
'Electronics, Books, Radios'    Italian Leather-Style Chesterton Cover for NOOK Reader  161561  4'''


groups = [item.split("' ") for item in data.split('\n')]
grouped_data = {}

for group in groups:
    item = [group[1].strip()]
    group = group[0].strip("'")
    if group not in grouped_data:
        grouped_data[group] = item
    else:
        grouped_data[group] += item

def topN(data, n):
    data = [item.split() for item in data]
    data = sorted(data, key=lambda x: float(x[-1]), reverse=True)[:n]
    data = [' '.join(item) for item in data]
    return data

result = {}
for k, v in grouped_data.items():
    result[k] = topN(v, 2)

final_result = [': '.join([group1, item1]) for group1, value1 in result.items() for item1 in value1]

Answer 3

也许不是一个有效但可以理解的解决方案：

您想要每个元素的最高结果，所以首先我们需要识别元素。我们通过在'上拆分来实现这一点，因为这是最简单的指示符，第一个'中的空字符串将被丢弃(1:)。

separated = [element.split("'")[1:] for element in data]

由于我们对第一个字符串标识的项感兴趣，字典似乎是一个合适的数据结构。

from collections import defaultdict
data_dict = defaultdict(list)
for line in separated:
    data_dict[line[0]].append(line)

现在我们有了一种很好的格式，可以对二叉树进行排序。

data_dict.keys()：data_dictkey.sort(key=lambda key_string: key_string.split()-1，reverse=True)中的密钥

从这本词典中可以很容易地复制我们的结果：

k = 2
results = []
for key in data_dict.keys():
    results.extend(data_dict[key][:k])

关键是要使用合适的数据结构，这里有一个字典。这里有一个简短的解决方案：

# make a dict 
from collections import defaultdict
data_dict = defaultdict(list)
for line in data:
    data_dict[line.split("'")[1]].append(line)


# function working on the dict:
def top_results(data_dict, k):
    results = []
    for key in data_dict.keys():
        results.extend(data_dict[key][:k])
    return results

但是，更适合继续使用字典，而不是返回不合适的列表。

概括地说：

1. 找出合适的数据结构，这里是一个适合的dict。
2. 获取您的密钥，split("'")将为此工作
3. 以很好的格式重新组织数据
4. 使用list.sort对您的列表进行排序。key是必需的，这里我们只使用最后一个单词str.split()[-1]，因为这是您的排名。