Reorder dictionary in python according to a list of values

Question

Let us consider a dictionary:

sample_dict={1:'r099',2:'g444',3:'t555',4:'f444',5:'h666'}

I want to re-order this dictionary in an order specified by a list containing the order of the dictionary keys that I desire. Let us say the desired order list is:

desired_order_list=[5,2,4,3,1]

So, I want my dictionary to appear like this:

{5:'h666',2:'g444',4:'f444',3:'t555',1:'r099'}

If I can get a list of values that is fine too. Meaning, the result can be this:

['h666','g444','f444','t555','r099']

How do I achieve this in the least complex way possible?

Answer 1

Answer for Python 3.6+

Guido has assured dictionaries would be ordered from Python 3.7 onwards, and they already were as an experimental feature in 3.6. The answer has already been expanded on in Fastest way to sort a python 3.7+ dictionary.

In this case, building a new dict with simple dictionary comprehension based on the items contained in the desired_order_list will do the trick.

sample_dict = {1: 'r099', 2: 'g444', 3: 't555', 4: 'f444', 5: 'h666'}
print(sample_dict)
>>> {1: 'r099', 2: 'g444', 3: 't555', 4: 'f444', 5: 'h666'}

desired_order_list = [5, 2, 4, 3, 1]

reordered_dict = {k: sample_dict[k] for k in desired_order_list}
print(reordered_dict)
>>> {5: 'h666', 2: 'g444', 4: 'f444', 3: 't555', 1: 'r099'}

Answer 2

If you're using an OrderedDict, you can do

for key in [5,2,4,3,1]:
    my_ordered_dict[key] = my_ordered_dict.pop(key)

This reinserts everything in your ordered dict in the sequence you want, such that later you can do

my_ordered_dict.values()

And get the list you suggested in the question.

If you wrap the reinsertion in a try: ...; except KeyError: pass, you can reorder an OrderedDict even if not all the keys in your list are present.

Answer 3

Python dictionaries are unordered.

Use OrderedDict instead.