在字典中找到第 n 个最大值的键

Question

given a dictionary like this: example_dict ={"mark":13, "steve":3, "bill":6, "linus":11}

finding the key with max value is easy using max(example_dict.items(), key=operator.itemgetter(1)) and min value using min(example_dict.items(), key=operator.itemgetter(1))

What's the easiest way to find the key with the n-th largest value? eg the key with the 2nd largest value here is linus

Answer 1

Use nlargest :

import heapq

example_dict ={"mark":13, "steve":3, "bill":6, "linus":11}

*_, res = heapq.nlargest(2, example_dict, key=example_dict.get)
print(res)

Output

linus

From the documentation:

Return a list with the n largest elements from the dataset defined by iterable. key, if provided, specifies a function of one argument that is used to extract a comparison key from each element in iterable (for example, key=str.lower).

A note on performance, also from the documentation:

perform best for smaller values of n. For larger values, it is more efficient to use the sorted() function. Also, when n==1, it is more efficient to use the built-in min() and max() functions. If repeated usage of these functions is required, consider turning the iterable into an actual heap.

Note that it returns a list, that is why you discard the first n-1 elements

Answer 2

Use QuickSelect algorithm. It works in O(n) on average

Answer 3

Something like this:

def nth_largest_key(di, n):
    sorted_items = sorted(di.items(), key=lambda item: item[1],
                          reverse=True)
    return sorted_items[n-1][0]


input_di = {"mark":13, "steve":3, "bill":6, "linus":11}
print(nth_largest_key(input_di, int(input().strip())))