Group key-value pairs and get count using Counter in python 3

Question

I have a list of dictionaries like this:

res = [{"isBlack": "yes"} , {"isWhite": "no"} , {"isRed": "yes"} , {"isWhite": "yes"} , {"isRed": "no"} , {"isBlack": "yes"}]

I need to group res by key-value pair and get their count using Counter, to look like this:

Counter({"isBlack:yes": 2 , "isWhite:no": 1, "isWhite:yes": 1 , "isRed:no": 1 , "isRed:yes": 1}) 

I tried this: count = Counter(res) , but getting error like:

TypeError: unhashable type: 'dict'

Is there something else I could try?

Answer 1

You just need to do some preprocessing in a generator expression to convert the dicts to strings.

print(Counter(f"{next(iter(d))}:{d[next(iter(d))]}" for d in res))

next(iter(d)) is to get the first key in a dictionary (which happens to be the only one here).

Answer 2

You can use the dict.popitem method to obtain the item tuple in each sub-dict first and then join the tuple into a colon-delimited string to pass on to Counter :

Counter(':'.join(d.popitem()) for d in res)

This returns:

Counter({'isBlack:yes': 2, 'isWhite:no': 1, 'isRed:yes': 1, 'isWhite:yes': 1, 'isRed:no': 1})

Alternatively, instead of using a colon-delimited string as a key, it would be more idiomatic to make the key-value tuples as generated by the dict.items() method the keys:

Counter(i for d in res for i in d.items())

This returns:

Counter({('isBlack', 'yes'): 2, ('isWhite', 'no'): 1, ('isRed', 'yes'): 1, ('isWhite', 'yes'): 1, ('isRed', 'no'): 1})