Title: Expanded dictionary inversion
Submitter: Jonathan Knoll (other recipes)
Last Updated: 2006/07/11
Version no: 1.0
Category: Shortcuts

Description:

Invert different types of dictionaries with mixed data types as values.

Source: Text Source

def invert1(d):
    dd = {}
    for k, v in d.items():
        if not isinstance(v, (tuple, list)): v = [v]
        dd.update( [(vv, dd.setdefault(vv, []) + [k]) for vv in v] )
    return dd


def invert2(d):
    dd = {}
    for k, v in d.items():
        if not isinstance(v, (tuple, list)): v = [v]
        [dd.setdefault(vv, []).append(k) for vv in v]
    return dd

Discussion:

I just wanted to add a few more possibilities to the inverters in these recipes:

   http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/252143
   http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/415100

   invert1({'A': [1, 1]}) --> {1: ['A']}
   invert2({'A': [1, 1]}) --> {1: ['A', 'A']}

   {'A': (1,), 'C': (3, 3), 'B': (2, 4)}
   {'A': [3, 2, 1], 'C': [3, 2], 'B': [1, 4]}
   {'A': 2, 'C': 4, 'B': 5, 'D': 5}
   {'A': 2, 'C': 4, 'B': 5, 'D': [5, 3]}
   {'A': [1, 2, 3], 'B': 4}