How Can I Count Occurrences Of Values In A List Of Dicts?

I have this list of dicts: [{'Description': 'LARCENY'}, {'Description': 'LARCENY'}, {'Description': 'BURGLARY'}, {'Description': 'ROBBERY - STREET'}, {'Description': 'COMMON ASSAUL

Solution 1:

While your data structure doesn't make sense as noted above, you can solve this easily using the Counter class from collections.

from collections import Counter

crimes = [{'Description': 'LARCENY'}, {'Description': 'LARCENY'}, {'Description': 'BURGLARY'}, {'Description': 'ROBBERY - STREET'}, {'Description': 'COMMON ASSAULT'}, {'Description': 'COMMON ASSAULT'}, {'Description': 'AUTO THEFT'}, {'Description': 'AUTO THEFT'}, {'Description': 'ROBBERY - STREET'}, {'Description': 'COMMON ASSAULT'}, {'Description': 'COMMON ASSAULT'}, {'Description': 'BURGLARY'}, {'Description': 'BURGLARY'}, {'Description': 'LARCENY'}, {'Description': 'ROBBERY - COMMERCIAL'}, {'Description': 'COMMON ASSAULT'}, {'Description': 'COMMON ASSAULT'}, {'Description': 'COMMON ASSAULT'}]

c = Counter()
for item in crimes:
    c[item["Description"]] += 1

print(c)

This gives the output of:

Counter({'COMMON ASSAULT': 7, 'BURGLARY': 3, 'LARCENY': 3, 'AUTO THEFT': 2, 'ROBBERY - STREET': 2, 'ROBBERY - COMMERCIAL': 1})

I'd recommend looking at the Counter class whenever you want to count things.

Solution 2:

Looks like you want to maintain the order of occurrence of the crimes as well.

So, use collections.OrderedDict instead of normal dict.

>>> from collections import OrderedDict
>>> counter = OrderedDict()
>>> for item in data:
...     if 'Description' in item:
...         counter[item['Description']] = counter.get(item['Description'], 0) + 1

Now, just construct a new dictionary with each and every key, value pair out of the counter, like this

>>> from pprint import pprint
>>> pprint([{k: v} for k, v in counter.items()])
[{'LARCENY': 3},
 {'BURGLARY': 3},
 {'ROBBERY - STREET': 2},
 {'COMMON ASSAULT': 7},
 {'AUTO THEFT': 2},
 {'ROBBERY - COMMERCIAL': 1}]

---

From the comments,

After I get the desired output I will need to separate the keys and the values into diferent lists,

Then, don't create list of dictionaries. Directly create two lists, with keys and values, from the counter itself, like this

>>> list(counter.keys())
['LARCENY', 'BURGLARY', 'ROBBERY - STREET', 'COMMON ASSAULT', 'AUTO THEFT', 'ROBBERY - COMMERCIAL']
>>> list(counter.values())
[3, 3, 2, 7, 2, 1]

Solution 3:

Given the result you've got so far...

>>> result = {'LARCENY' : 3, 'BURGLARY' : 2, 'ROBBERY - STREET' : 3}
>>> result = [{k:v} for k,v in result.items()]
>>> result
[{'BURGLARY': 2}, {'LARCENY': 3}, {'ROBBERY - STREET': 3}]