Python 列表分组依据

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前 k 个。前 2 名应该给出以下结果:

'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

添加我尝试过的任何东西:

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

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

在这里，我将“k”作为命令行参数传递给 python 文件。

Answer 1

使用迭代器之类的，可以获得相对高效的性能。注意:这使用标准的 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)