Have you ever need to invert a dictionary with value being a list in Python?
Here is what I mean. We need to convert the following dict:
{ "apple" : [ "green", "red" ],
"watermelon" : [ "green" ],
"strawberry" : [ "red" ],
"lemon" : [ "green", "yellow" ] }
To a new dict as below:
{ 'green' : ['apple', 'watermelon', 'lemon'],
'red' : ['apple', 'strawberry'],
'yellow' : ['lemon'] }
Here's my solution which using the defaultdict from collections:
>>> from collections import defaultdict
>>> a_dict = { "apple" : [ "green", "red" ], "watermelon" : [ "green" ], "strawberry" : [ "red" ], "lemon" : [ "green", "yellow" ] }
>>> b_dict = defaultdict(list)
>>> for k,v in a_dict.items():
... for k1 in v:
... b_dict[k1].append(k)
...
>>> b_dict
defaultdict(<class 'list'>, {'green': ['apple', 'watermelon', 'lemon'], 'red': ['apple', 'strawberry'], 'yellow': ['lemon']})
There is another way that simplies what we have above:
>>> from collections import defaultdict
>>> a_dict = { "apple" : [ "green", "red" ], "watermelon" : [ "green" ], "strawberry" : [ "red" ], "lemon" : [ "green", "yellow" ] }
>>> b_dict = defaultdict(list)
>>> { b_dict[k1].append(k) for k,v in a_dict.items() for k1 in v }
>>> b_dict
Alright, hope this helps!!