Sort keys in dictionary by value in a list in Python

Question

I have seen this post and this post as well as many others, but haven't quite found the answer to my question nor can I figure it out.

I have a dictionary of lists. For example it looks like:

Dict = {'a':[1,2,3,4], 'b':[9,8,7,6], 'c':[8,5,3,2]}

I want to return a list of the keys sorted (descending/reverse) based on a specific item in the lists. For example, I want to sort a,b,c based on the 4th item in each list.

This should return the list sorted_keys = ['b','a','c'] which were sorted by values [6,4,2] .

Make sense? Please help...thanks!

Answer 1

Supply a key function, a lambda is easiest, and sort reversed:

sorted(Dict.keys(), key=lambda k: Dict[k][3], reverse=True)

The key function tells sorted what to sort by ; the 4th item in the value for the given key.

Demo:

>>> sorted(Dict.keys(), key=lambda k: Dict[k][3], reverse=True)
['b', 'a', 'c']