How to get the max N elements

Question

I know how to get a single max:

m = max([1,2])
2

How would I get the max n elements? For example:

m = max([1,2,3,4,5], n=2)
[4,5]

Boa · Answer 1 · 2015-03-14T22:02:25.967

13

import heapq
input_list = [1,2,3,4,5]
number_of_elements = 3
heapq.nlargest(number_of_elements, input_list)

For more info, here are the heap queue algorithm docs

edited Mar 14 '15 at 22:02

answered Mar 14 '15 at 21:56

Boa

1

By far the best approach! – Alex Martelli Mar 14 '15 at 21:58
1

You can see a discution about time complexity here : http://stackoverflow.com/q/23038756/4660239 – Florian Prud'homme Mar 14 '15 at 22:29

score 5 · Answer 2 · answered Mar 14 '15 at 21:55

5

Here's one way to implement it - sort the list, then slice the first n elements.

def maxN(elements, n):
    return sorted(elements, reverse=True)[:n]

answered Mar 14 '15 at 21:55

Brionius

This is not the most efficient way to find the max n elements, since sorting the entire list may not be necessary if all you need is the top few values. – Daniel Jan 07 '19 at 00:21

score 1 · Answer 3 · edited May 23 '17 at 11:50

1

If you want to beat the performance of a sorting algo you need to use a select algorithm (like QuickSelect)

This reduces the average complexity from O(n log n) (in quicksort) to O(n) (in quickselect).

edited May 23 '17 at 11:50

Community

answered Mar 14 '15 at 21:57

3 Answers3