I have a list of dicts and would like to design a function to output a new dict which contains the sum for each unique key across all the dicts in the list.
For the list:
[
{
'apples': 1,
'oranges': 1,
'grapes': 2
},
{
'apples': 3,
'oranges': 5,
'grapes': 8
},
{
'apples': 13,
'oranges': 21,
'grapes': 34
}
]
So far so good, this can be done with a counter:
def sumDicts(listToProcess):
c = Counter()
for entry in listToProcess:
c.update(entry)
return (dict(c))
Which correctly returns:
{'apples': 17, 'grapes': 44, 'oranges': 27}
The trouble comes when the dicts in my list start to contain nested dicts:
[
{
'fruits': {
'apples': 1,
'oranges': 1,
'grapes': 2
},
'vegetables': {
'carrots': 6,
'beans': 3,
'peas': 2
},
'grains': 4,
'meats': 1
},
{
'fruits': {
'apples': 3,
'oranges': 5,
'grapes': 8
},
'vegetables': {
'carrots': 7,
'beans': 4,
'peas': 3
},
'grains': 3,
'meats': 2
},
{
'fruits': {
'apples': 13,
'oranges': 21,
'grapes': 34
},
'vegetables': {
'carrots': 8,
'beans': 5,
'peas': 4
},
'grains': 2,
'meats': 3
},
]
Now the same function will give a TypeError because the counter can't add two Dicts.
The desired result would be:
{
'fruits': {
'apples': 17,
'oranges': 27,
'grapes': 44
},
'vegetables': {
'carrots': 21,
'beans': 12,
'peas': 9
},
'grains': 9,
'meats': 6
}
Any ideas on how to do this in a reasonably efficient, Pythonic, generalizable way?
Thanks!
In Python, a Nested dictionary can be created by placing the comma-separated dictionaries enclosed within braces.
In python, if we want a dictionary in which one key has multiple values, then we need to associate an object with each key as value. This value object should be capable of having various values inside it. We can either use a tuple or a list as a value in the dictionary to associate multiple values with a key.
I would do this by performing a recursive merge on a recursively defined collections.defaultdict
object.
from collections import defaultdict
def merge(d, new_d):
for k, v in new_d.items():
if isinstance(v, dict):
merge(d[k], v)
else:
d[k] = d.setdefault(k, 0) + v
# https://stackoverflow.com/a/19189356/4909087
nested = lambda: defaultdict(nested)
d = nested()
for subd in data:
merge(d, subd)
Using default_to_regular
to convert it back, we have:
default_to_regular(d)
# {
# "fruits": {
# "apples": 17,
# "oranges": 27,
# "grapes": 44
# },
# "vegetables": {
# "carrots": 21,
# "beans": 12,
# "peas": 9
# },
# "grains": 9,
# "meats": 6
# }
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