Returning the highest 6 names in a List of tuple in Python

Question

Please I want to return first 6 names (only the names) with the highest corresponding integers from the list of tuple below. I have been able to return all the names from highest (sms) to lowest (boss).

[('sms', 10), ('bush', 9), ('michaels', 7), ('operations', 6), ('research', 5), ('code', 4), ('short', 3), ('ukandu', 2), ('technical', 1), ('apeh', 1), ('boss', 1)]

Thank you.

Answer 1

heapq.nlargest is what you want here:

import heapq
from operator import itemgetter
largest_names = [x[0] for x in heapq.nlargest(6,your_list,key=itemgetter(1))]

It will be more efficient than sorting as it only takes the biggest elements and discards the rest. Of course, it is less efficient than slicing if the list is pre-sorted for other reasons.

Complexity:

• heapq: O(N)
• sorting: O(NlogN)
• slicing (only if pre-sorted): O(6)

Explanation:

heapq.nlargest(6,your_list,key=itemgetter(1)) 

This line returns a list of (name,value) tuples, but only the 6 biggest ones -- comparison is done by the second (index=1 --> key=itemgetter(1)) element in the tuple.

The rest of the line is a list-comprehension over the 6 biggest name,value tuples which only takes the name portion of the tuple and stores it in a list.

---

It might be of interest to you that you could store this data as a collections.Counter as well.

d = collections.Counter(dict(your_list))
biggest = [x[0] for x in d.most_common(6)]

It's probably not worth converting just to do this calculation (that's what heapq is for after all ;-), but it might be worth converting to make the data easier to work with.

Answer 2

data=[('sms', 10), ('bush', 9), ('michaels', 7), ('operations', 6), ('research', 5), ('code', 4), ('short', 3), ('ukandu', 2), ('technical', 1), ('apeh', 1), ('boss', 1)]
return [x[0] for x in sorted(data, key=lambda x: x[1], reverse=True)[0:6]]

Which does following:

• sorted returns data sorted using key function. Since standard sorting order is from ascending, reverse=True sets it do descending;
• lambda x: x[1] is anonymous function which returns second element of the argument (of a tuple in this case); itemgetter(1) is nicer way to do this, but requires additional imports;
• [0:6] slices first 6 elements of the list;
• [x[0] for x in ... ] creates a list of first elements of each passed tuple;