Sorting tuples in python based on their values [duplicate]

问题

This question already has answers here:

How to sort (list/tuple) of lists/tuples by the element at a given index? (10 answers)

How to find most common elements of a list? (10 answers)

Closed 5 years ago.

I am trying to print the top 10 frequent words using the following code. However, its not working. Any idea on how to fix it?

def reducer_count_words(self, word, counts):
    # send all (num_occurrences, word) pairs to the same reducer.
    # num_occurrences is so we can easily use Python's max() function.
    yield None, (sum(counts), word)




# discard the key; it is just None
def reducer_find_max_10_words(self, _, word_count_pairs):
    # each item of word_count_pairs is (count, word),
    # so yielding one results in key=counts, value=word

        tmp = sorted(word_count_pairs)[0:10]
        yield tmp

回答1:

tmp = sorted(word_count_pairs, key=lambda pair: pair[0], reverse=True)[0:10]

Explanation:

• The key parameter of sorted() allows you to run a function on each element before comparison.
• lambda pair: pair[0] is a function that extracts the number from your word_count_pairs.
• reverse sorts in descending order, instead of ascending order.

Sources:

• https://wiki.python.org/moin/HowTo/Sorting#Key_Functions
• https://docs.python.org/2/library/functions.html#sorted

---

aside: If you have many different words, sorting the entire list to find the top ten is inefficient. There are much more efficient algorithms. The most_common() method mentioned in another answers probably utilizes a more efficient algorithm.

回答2:

Use collections.Counter and its most_common method:

>>>from collections import Counter
>>>my_words = 'a a foo bar foo'
>>>Counter(my_words.split()).most_common()
[('foo', 2), ('a', 2), ('b', 1)]

回答3:

Use collections.most_common()

Example:

most_common([n])
Return a list of the n most common elements and their counts from the most common to the least. If n is not specified, most_common() returns all elements in the counter. Elements with equal counts are ordered arbitrarily:

>>> from collections import Counter
>>> Counter('abracadabra').most_common(3)
[('a', 5), ('r', 2), ('b', 2)]

来源：https://stackoverflow.com/questions/23918852/sorting-tuples-in-python-based-on-their-values