How to make a Custom Sorting Function for Dictionary Key Values?

January 7, 2022

I have a dictionary whose key values are kind of like this,

CC-1A
CC-1B
CC-1C
CC-3A
CC-3B
CC-5A
CC-7A
CC-7B
CC-7D
SS-1A
SS-1B
SS-1C
SS-3A
SS-3B
SS-5A
SS-5B

lst = ['CC-1A', 'CC-1B', 'CC-1C', 'CC-3A', 'CC-3B', 'CC-5A', 'CC-7A', 'CC-7B', 
       'CC-7D', 'SS-1A', 'SS-1B', 'SS-1C', 'SS-3A', 'SS-3B', 'SS-5A', 'SS-5B']
d = dict.fromkeys(lst)

^Not exactly in this order, but in fact they are all randomly placed in the dictionary as key values.

Now, I want to sort them. If I use the built in function to sort the dictionary, it sorts all the key values according to the order given above.

However, I want the dictionary to be first sorted based upon the values after the – sign (i.e. 1A, 1B, 1C etc.) and then based upon the first two characters.

So, for the values given above, following would be my sorted list,

    CC-1A
    CC-1B
    CC-1C
    SS-1A
    SS-1B
    SS-1C
    CC-3A
    CC-3B
    SS-3A
    SS-3B
    CC-5A
    and so on

First, sorting is done based upon the "4th" character in the keys. (that is, 1, 3, etc.)
Then sorting is done based upon the last character (i.e. A, B etc.)
Then sorting is done based upon the first two characters of the keys (i.e. CC, SS etc.)

Is there any way to achieve this?

>Solution :

You could use a custom function that implements your rule as sorting key:

def get_order(tpl):
    s = tpl[0].split('-')
    return (s[1][0], s[0], s[1][1])


out = dict(sorted(d.items(), key=get_order))

Output:

{'CC-1A': None, 'CC-1B': None, 'CC-1C': None, 'SS-1A': None, 'SS-1B': None, 'SS-1C': None, 'CC-3A': None, 'CC-3B': None, 'SS-3A': None, 'SS-3B': None, 'CC-5A': None, 'SS-5A': None, 'SS-5B': None, 'CC-7A': None, 'CC-7B': None, 'CC-7D': None}