how do I sort a python list of dictionaries given a list of ids with the desired order?

Question

I've got a list of dictionaries like this:

users = [{'id':1, 'name': 'shreyans'}, {'id':2, 'name':'alex'}, {'id':3, 'name':'david'}]

and a list of ids with the desired order:

order = [3,1,2]

What's the best way to order the list users by the list order ?

Answer 1

users = [{'id':1, 'name': 'shreyans'},
         {'id':2, 'name':'alex'},
         {'id':3, 'name':'david'}]
order = [3,1,2]

users.sort(key=lambda x: order.index(x['id']))

Answer 2

If the lists are really big:

userd = {d['id']:d for d in users}
sortedusers = [userd.get(o) for o in order]

This is O(2n) . A solution using sort only will be O(n^3.log(n)) (sort is nlogn , finding position of every id in list is O(n^2) ), which is clearly worse for larger lists. For smaller lists (such as 3 items), the low overhead of not creating a new data structure will make it faster; conversely if you keep sorting by new order specifications, the overhead of making the new dict will quickly amortise.

Answer 3

使用自定义键排序：

users.sort(key=lambda x: order.index(x['id']))